Path Dependence

Path dependence is the way an outcome gets locked in by the sequence of past choices rather than by the merits of the alternatives available today. Once enough has been built on an early decision — tooling, trained habit, compatible formats, the code that assumes it — switching to an objectively better option can cost more than staying put, even when everyone agrees the alternative is superior in isolation. The mechanism is increasing returns to adoption: each additional dependent makes the incumbent cheaper relative to its rivals, the same pull that gives a Network Effect its self-reinforcing shape.

The standard illustration is the QWERTY keyboard, popularised by Paul David's 1985 argument that a layout shaped by an 1870s typewriter's jams outlived the jam by a century through sheer lock-in. David's mechanism is mechanical, not ergonomic: typebars clashed and stuck when adjacent keys were struck in rapid succession, so Sholes separated the commonest letter pairs. The familiar claim that QWERTY was designed to slow typists down is itself folklore, fittingly enough for a case study in received histories, and later work — including Kay's 2011 reconstruction — supports the anti-jamming account. The example is more contested than the retelling suggests: Liebowitz and Margolis re-examined the typing-speed trials behind the claim that Dvorak is meaningfully faster and found the evidence thin, concluding QWERTY may simply have been good enough that nobody's switching costs were ever repaid. Both sides agree on the mechanism; they disagree on whether this fence, in the sense of Chesterton's Fence, was load-bearing at all — the part the example is usually cited to skip.

That caution generalises past keyboards. "Nobody would design it this way today" is true of almost every mature system and is not, by itself, a case for tearing it out; it omits the switching cost, which Technical Debt exists to track and a staged Deprecation exists to pay down on purpose. The Provenance of a decision — why the path was taken, not merely that it was — is what turns "we would not choose this" into an argument rather than a complaint.