I suffer from sunk-cost fallacy. This is the phenomenon whereby you remain committed to a previous choice because of what you have ’sunk’ or invested in it, even though new evidence suggests a different option would cost you less.
It shows up for me when I have made a plan to do something, and then plans change, for example when travelling or making plans for the weekend. I remain psychologically committed to the original plan even though it might not make sense any more. I suffer from sunk-cost fallacy because I am a human, and this is a common bias that we suffer.
Sunk-cost fallacy also shows up in design. It is when we remain committed to one option which we have invested time, resource and psychological energy in, even when a better answer emerges. If our priority is to get our job done, then making decisions purely on the basis of sunk costs might be sensible. But if our priority is getting the right design, then the sunk-cost is a poor guide, as it fails to account for the total cost of having the wrong answer.
Where money is concerned the distraction is how much you have already spent, when the real concern should be how much you still have to spend. For major projects, where we routinely, systematically underestimate the future costs, the risk of sunk-cost fallacy affecting judgement is even greater.
Whether we are making plans for the weekend or plans for a new railway, look out for sunk-cost fallacy!