Comparison
RewritevsSunk cost fallacy
Rewrite
you decided to start again, and the old system kept receiving feature requests the whole time.
Replacing a system with a new implementation rather than evolving the existing one. It is occasionally correct — when the platform is unsupported, the model is fundamentally wrong, or the thing is small — and it is usually chosen for the wrong reason, which is that reading the old code is unpleasant. The costs that get missed are the undocumented behaviour the old system accumulated and the feature freeze that never actually holds.
Full entry →Sunk cost fallacy
the migration has taken eight months, so the argument for continuing was that it has taken eight months.
Continuing to invest because of what has already been spent, which is money and time you cannot recover either way. The only sound question is the forward one: given where we are now, is this the best use of the next three months. It is unusually hard in engineering because abandoning work feels like admitting the earlier decision was wrong, which is exactly the feeling the fallacy runs on.
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