I won't do that again
Most of us go through life learning from our mistakes. If we do something with unpleasant consequences, we try not to do the same again. Depending on the seriousness of the consequences, we may repeat the mistake several times until the penny finally drops.
However, there are some mistakes that you only make once and those are the ones I'd like to tell you about here. I have three at the moment, but may well add to the list later.
Mistake 1) When I was young I picked up one of my mother's knitting needles and did my impression of a strong man by bending it through 90 degrees. She was in the kitchen making tea, so I thought I'd just bend it back straight before she returned. Big mistake; for some reason knitting needles don't bend back straight, so I finished up with a good hiding.
Mistake 2) Somebody once told me that the best way to check if a 9 volt battery was dead, was for me to put my tongue across the terminals. Big mistake; the battery was live and gave me such a shock I almost bit my tongue in half. It needed five stitches to hold it together.
Mistake 3) I was riding my bike down the road one day when I had a thought. I wondered what would happen if I crossed my hands over on the handlebars, so I tried it. Big mistake; in less than a heart beat I was face down on the road with blood and snot everywhere. I lost three teeth and still have a scar on my forehead.