People make mistakes every day. Every single day. That's not what does it.
People make bigger mistakes, often. Or at least, every once in a while. The fact that they're bigger, that's not what does it, either.
It's getting caught. That's what does it. Making a big(ger) mistake, and getting caught.
A figure of authority is standing over you, looking through you. He's waving a finger back and forth. Saying over and over, "Busted. Just... busted." Even more- he assures you that, if he really wanted to, he could break you down much worse. He could really fuck shit up for you. And you hate him for a minute, and you hate yourself for a lot longer than that.
Getting caught. That's what does it.
Afterward, all of your self-confidence runs away from you. Runs screaming away. Like you were the fucking plague. It comes back with time- but definitely not right away. And your calves grow exponentially from all that tip-toeing around.