Be courageous enough to admit your own self-sabotage against your manly gearhead image!
My dumbest move ever was in high school, when my Dodge omni's engine was making some horrendous noise. I chose to ignore the sound of a water pump eating $#!t. The engine got so hot that I couldn't even shut it off. It dieseled until it siezed. The best thing to come out of it though was my purchase of my first German car a '65 bug. Learned from the experience thank God.

Let's hear your story!