I suspect this dynamic is a big part of why Joel Spolsky jokes about transforming from a technical leader into an amateur psychologist. We are all lying to ourselves first and to others second.
Or as Feynman said, the trick is not to fool yourself, and you’re the easiest person to fool.
Or a personal favorite, unattributed: I know the guy who made this plan [me] and he’s full of shit.
Some things you can cut corners and save time.
Some things, when you cut the corners off you also cut your fingers off.
We have all promised that we will “fix it later”. But whatever we do now is what’s done. Fixing it later is a promise whose resolution is often not in our control.