Measure twice, and cut once is a reminder to double-check your workings. Not bad advice.
Quentin Tarantino famously didn’t go to film school. Instead, he learned as he went along. “I realised that I didn’t have what I thought I had.” And as hard as that was to take, it was ok, because Tarantino treated his failure as an education. Learning on the job was film school.
The first time you measure you have no clue what you are measuring. And at that point you have options:
Hide the fact that it’s shit.
Move on to measure it all over again.
Quit and hire someone who knows what the f**ck they are doing.
Learning that you don’t have what you thought you had, that’s an education. The question is. What are you going to do about it?