Not taking the free PhD path I was offered.

I didn’t stay 20 years in the Marines.

I would say it was trusting those having average degrees of untrustworthiness when what I actually needed was zero degrees.

This was not so much of a problem until I had founded my company where it really means the most. You can become kind of numb to the average stuff as your previous employment does progress, where you pretty much have to get accustomed to your main financial "partner" not being perfectly aligned from the beginning.