Ground Truth
The measurement that arbitrates, as opposed to the artifact that merely reports.
Ground truth is the observation that settles a question, as distinct from the many artifacts that describe it. Most debugging confusion comes from treating a report as a measurement.
Examples of the distinction are everywhere. A build tool's summary table is a report; the actual script tags in the served HTML are ground truth. A hosting platform's "mergeable" flag is a report; performing the merge locally is ground truth. A green exit code is a report; the count of tests that actually ran is ground truth — a filter that matched nothing exits zero. A comment claiming an invariant is a report; the type system is ground truth.
The habit worth building is to ask, for any claim you are about to act on, what would I have to look at to be wrong about this? — then look at that. It is usually cheaper than the reasoning it replaces.
Ground truth also has a staleness dimension. A measurement is only about the thing you measured, at the moment you measured it. Verifying against a server compiled before your change, or a cached artifact from a prior state, produces a real number about the wrong world. Restart, rebuild, refetch before every claim you intend to stand behind.
See also8
Falsifiability
A claim is only worth something if you know what observation would refute it.
Method46 connections
Observability
How much of a system's internal state can be inferred from what it emits.
Method24 connections
Reproducible Case
The smallest set of steps that reliably produces a fault, and the unit of real debugging.
Method25 connections
Determinism
The property that identical inputs produce identical outputs, and the foundation of caching and verification.
Systems & Tooling56 connections
Instrumentation
Adding measurement to code so its execution can be observed, and the distortions that introduces.
Testing & Verification17 connections
Silent Failure
A failure that produces no signal, so the absence of an error reads as success.
Method63 connections
Root Cause Analysis
Escalating past the visible symptom until you find the layer that actually produced it.
Method49 connections
Vacuous Truth
A statement that holds only because its subject set is empty — a green result that measured nothing.
Method26 connections
Related2
Nearby in the graph rather than deliberately chosen. Looser, sometimes surprising.
Linked from94
- Adversarial ReviewAgents & Language Models
Reviewing work with an explicit mandate to refute it, from a perspective that did not produce it.
- Automatic Speech RecognitionAgents & Language Models
Turning audio into text, and the reasons real-world accuracy is set by the signal more than by the model.
- Automation BiasMethod
Over-trusting an automated recommendation, including against available contrary evidence.
- BackronymMeaning & Society
An expansion invented after the fact to fit letters that already existed as a word or acronym.
- Base Rate FallacyMethod
judging a specific case from vivid evidence while discounting how common the categories actually are.
- Betteridge's Law of HeadlinesMethod
any headline phrased as a question can safely be answered "no".
- Big-O NotationComputation & Algorithms
A coarse language for how an algorithm's cost grows as its input grows.
- Bone RemodelingBody & Medicine
Living bone is continuously resorbed and rebuilt, which is why fractures heal and why healing runs in stages.
- Broken Windows TheoryMeaning & Society
The hypothesis that visible disorder invites serious crime, and the long dispute over whether the evidence supports it.
- BundlerWeb Platform
The tool that resolves an application's modules into the files a browser downloads.
- Cargo CultMethod
Imitating the visible form of a practice while the mechanism that made it work is absent.
- Character EncodingSystems & Tooling
The mapping between characters and bytes, and the source of a specific family of invisible bugs.
- Chekhov's GunMeaning & Society
The convention that a conspicuously introduced story element must pay off later.
- Code SigningSystems & Tooling
Cryptographically attesting who produced a binary, and the operating-system checks built on it.
- Code SplittingWeb Platform
Dividing an application bundle so a page downloads only the code it needs.
- CollocationMeaning & Society
Words that habitually appear together more often than chance predicts, independent of any grammatical rule.
- Confidence TrickMeaning & Society
Fraud that obtains trust first, so the victim hands over the money themselves.
- Confirmation BiasMethod
The tendency to search for, interpret, and recall evidence in ways that favor what you already believe.
- ContainerizationSystems & Tooling
Packaging an application with its dependencies into an isolated, reproducible runtime unit.
- Continuous DeploymentVersion Control & Delivery
Automatically releasing every change that passes validation.
- DaemonSystems & Tooling
A long-running background process managed by the operating system's service supervisor.
- DataminingPlay & Games
Extracting a game's files to recover mechanics, content and numbers the developer never published.
- DispersionMatter & Energy
Refractive index varies with wavelength, so a medium bends colors by different amounts.
- EggcornMeaning & Society
A substitution that reanalyzes a phrase into a different but still-plausible meaning.
- Environmental StorytellingPlay & Games
Narrative carried by placed objects and world state rather than dialogue, completed by the audience's inference.
- Exhaustive ClaimMethod
A statement of the form "the last one" or "nothing else does this" — load-bearing, and only as good as the search behind it.
- Fair-Play MysteryMeaning & Society
The convention that a detective story must give the audience every clue it needs to solve the case.
- FalsifiabilityMethod
A claim is only worth something if you know what observation would refute it.
- Fan-Out and Fan-InAgents & Language Models
Splitting work across parallel workers and recombining their results.
- Fermi EstimationMethod
Reaching a defensible order-of-magnitude answer by decomposing a question into estimable factors.
- Flaky TestTesting & Verification
A test that passes and fails on identical input, and the most corrosive thing a suite can contain.
- Folk EtymologyMeaning & Society
Words reshaped to resemble familiar parts, and the false origin stories that reshaping invites.
- Fracture FixationBody & Medicine
Holding fractured bone still enough, and aligned well enough, for biology to do the repair.
- Fracture NonunionBody & Medicine
A fracture that stops progressing toward healing, usually because of motion, gap or lost blood supply.
- GlobSystems & Tooling
Wildcard pattern matching over filenames, similar enough to regular expressions to mislead.
- Grammatical GenderMeaning & Society
A noun classification system that forces agreement across a sentence and correlates only loosely with meaning.
- HallucinationAgents & Language Models
Fluent, confident output that is not grounded in anything real.
- Hanlon's RazorMethod
Never attribute to malice that which is adequately explained by stupidity.
- Illusory Truth EffectMethod
A claim feels more true the more times you've heard it, independent of any evidence for it.
- Inertial Frame of ReferenceMatter & Energy
A coordinate system in which an undisturbed body moves at constant velocity, and none is privileged.
- InstrumentationTesting & Verification
Adding measurement to code so its execution can be observed, and the distortions that introduces.
- Kuleshov EffectMeaning & Society
Juxtaposed shots produce a meaning that exists in neither shot alone.
- Least Recently Used CacheComputation & Algorithms
A fixed-capacity cache that evicts whichever entry has gone untouched the longest.
- LegibilityMeaning & Society
Making a system countable and administrable, at the cost of the local knowledge that made it work.
- LetterlockingMeaning & Society
Folding, slitting and sealing a letter so the sheet becomes its own tamper-evident envelope.
- MacGuffinMeaning & Society
An object that motivates a plot while remaining substantively irrelevant to it.
- Merge ConflictVersion Control & Delivery
Overlapping changes that a merge cannot combine automatically, requiring a decision.
- MetroidbrainiaPlay & Games
A subgenre where progress is gated by what the player has learned, not by an item or ability the character carries.
- Modern Monetary TheoryMeaning & Society
A macroeconomic account holding that a currency issuer is constrained by real resources and inflation rather than by revenue.
- Module GraphWeb Platform
The directed graph of imports that decides what code ends up where.
- Moist Wound HealingBody & Medicine
Wounds kept moist under an occlusive dressing re-epithelialize faster than wounds allowed to dry and scab.
- MondegreenMeaning & Society
A misheard phrase reanalyzed into something else that still makes sense, most often from song lyrics.
- Monty Hall ProblemMethod
A conditional-probability puzzle in which switching wins twice as often as staying.
- NociceptionBody & Medicine
The nervous system's detection of damaging stimuli, which is not the same thing as the experience of pain.
- ObservabilityMethod
How much of a system's internal state can be inferred from what it emits.
- Opponent Process TheoryDesign & Interface
Color is recoded after the cones into red-green, blue-yellow and light-dark opponent channels.
- Pascal's PrincipleMatter & Energy
Pressure applied to a confined fluid is transmitted undiminished throughout it.
- Percentage PointMethod
The unit of an absolute change in a percentage, and the gap between that and a relative change.
- Planned ObsolescenceMeaning & Society
designing or marketing a product for a shorter useful life than it could otherwise have.
- Plausible MechanismMethod
A causal explanation that was inferred rather than tested, and reads as more rigorous for being specific.
- Polarized LightMatter & Energy
Light whose electric field oscillates in a preferred orientation, and the filters that select for it.
- Premature OptimizationMethod
Spending effort making code fast before you know where it's actually slow trades clarity for speed you may not need.
- Principal-Agent ProblemMeaning & Society
Divergent interests and unequal information between whoever delegates and whoever acts.
- Prototype TheoryMeaning & Society
Categories are organized as graded resemblance to a best example rather than defined by necessary and sufficient conditions.
- Race ConditionTesting & Verification
A defect whose occurrence depends on the relative timing of concurrent operations.
- Regulatory CaptureMeaning & Society
Regulators coming to serve the industries they oversee, and why the word is often overused.
- Rent-SeekingMeaning & Society
Spending resources to capture existing value instead of creating new value.
- Reproducible CaseMethod
The smallest set of steps that reliably produces a fault, and the unit of real debugging.
- Right to RepairMeaning & Society
the movement for consumer and independent-shop access to the parts, tools, and information needed to fix a device.
- Rolling ResistanceMatter & Energy
The energy a rolling tire loses to deformation, and why more pressure stops helping.
- Root Cause AnalysisMethod
Escalating past the visible symptom until you find the layer that actually produced it.
- Rubber Duck DebuggingMethod
Explaining a problem aloud, in full detail, to a listener who cannot help — and finding the fault while explaining it.
- Secret ManagementSystems & Tooling
Storing, distributing, and rotating credentials without embedding them in code or history.
- Segmented SleepBody & Medicine
The claim that pre-industrial night sleep came in two blocks separated by a waking interval, and the dispute over how general that was.
- Selection BiasMethod
A sample distorted because inclusion in it was never random.
- Semantic SatiationMeaning & Society
A word repeated aloud until it briefly stops registering as meaningful.
- Sensitivity and SpecificityMethod
The two error rates of a test, and why neither answers the question a person actually asks.
- ShellSystems & Tooling
The interactive command interpreter, and a programming language with unusually sharp edges.
- ShibbolethMeaning & Society
A pronunciation or usage that reveals group membership, historically used as a test with lethal stakes.
- Silent FailureMethod
A failure that produces no signal, so the absence of an error reads as success.
- Specific Absorption RateMatter & Energy
The rate at which tissue absorbs radiofrequency energy, measured in watts per kilogram.
- SpeedrunPlay & Games
Completing a game as fast as possible under a ruleset the community defines, not the game.
- Spoiler EtiquettePlay & Games
The informal norms communities use to manage narrative disclosure around games still being played.
- Streetlight EffectMethod
Looking where the light is good rather than where the answer is.
- SubagentAgents & Language Models
A model instance spawned by another to handle a scoped task with its own context.
- Survivorship BiasMethod
Drawing conclusions from a sample already filtered by success.
- Terror Management TheoryMeaning & Society
The experimental claim that reminders of death increase defense of one's worldview and self-esteem.
- Time ZoneSystems & Tooling
Civil time is a political layer over solar time, and its rules change often enough to be data.
- Tragedy of the CommonsMeaning & Society
Hardin's parable of shared-resource collapse, and Ostrom's evidence that it is not inevitable.
- Truncation BiasMethod
Reading a truncated result as if it were the whole result, so every counterexample is invisible.
- Vacuous TruthMethod
A statement that holds only because its subject set is empty — a green result that measured nothing.
- Vapor-Compression RefrigerationMatter & Energy
A closed loop that moves heat by boiling and condensing a working fluid at two pressures.
- Watershed Blood SupplyBody & Medicine
Tissue fed by a single terminal or retrograde vessel has no redundancy, so injury there heals badly.
- Web Font LoadingWeb Platform
How custom typefaces are fetched and shown, and why the cost is easy to misattribute.