Not the person you asked, but I'll provide one.

Friend: "I have $X and want to buy a new car." Friend goes to a car dealer, realizes all new cars cost MUCH more than $X, and buys a new car anyway.

Friend a month later: "The interest, taxes, and payments are so expensive. I can barely pay my bills now!"

This friend is going to be car-poor for the next 5ish years due to this inability to stop and recalculate.

Here's an example. I haven't been interacting with a lot of people the past few years so took awhile to think of one.

Know some people who made a plan to buy a to be rental property and live in it until it's paid off. They spent months searching for one in a very specific area but never found one that met the criteria. The one said to back out, we've found out mid plan that it won't work. The other went through and bought a property anyways. Now they're fucked.