What is a mistake?

When I was in high school, I dated this girl. Actually, I dated a lot of girls, which collectively may constitute my favorite mistake, but I can think of one particular girl who truly represents all such mistakes. I dated this girl for quite awhile, and it was awesome. We had some really good times. But after awhile, I got bored or something. I remember becoming insanely discontent. Part of me wanted the relationship to be over and part of me was really, truly happy with things. As a result, I started treating her really badly. I would pick fights, intentionally “forget” things she had said, and change plans on her. I was very intentionally trying to make her break up with me, so I wouldn’t have to do it. And when she finally did, I was hurt more than I could have thought. I was desperately heartbroken. For a loooong time. I didn’t know what to do with all of my hurt, so I sat through it. I waited it out. And when I finally did get into another relationship, I did the exact same thing. And the next girl, too. And on and on.
So why would this be my favorite mistake? Because it was a mistake. Despite my intentions, it was unintentionally painful. And because I learned nothing from it. Could it even be called a mistake if it were somehow justified?
Yesterday, I went mini-golfing with my wife and my friend. My friend found an extra golf ball on the ground, so he picked it up. Almost immediately after that, a woman on the hole ahead of us hit her ball off the course, through the chain link fence, and across the street. My friend simply handed her the extra ball and smiled. When she turned around and walked away, my friend said, “Everything happens for a reason.”
The reason that my failed high school relationship is my favorite mistake is because it didn’t happen for a reason. Or rather, it happened for a reason (I certainly seemed to cause it), but such reasons served no purpose. In other words, I accomplished something entirely by accident that I had never intended to give to myself or to anyone else.
Maybe one could say that I must have learned something from that experience. I must have been changed and formed in some way, which I suppose is true. But then I suppose–if I’m not mistaken–there would be no mistakes. This is not to say that everything happens for a reason–a sentiment I simply cannot get on board with, mostly because I think it’s just too easy for fortunate people to say so. It is to say that there are no mistakes. Everything we do is on purpose, and mistakes are impossible. In order to truly be a mistake, such events would have to be entirely unforeseen and useless. They would cost time and gain nothing.
I can think of one pure mistake. One day, my father-in-law stood outside a store facing the parking lot. A woman approached him from behind and grabbed a healthy handful of his ass. Neither looked at the other, assuming that acquaintance was obvious. After a brief pause, they glanced at each other and realized that he was not her husband, as she had thought, and she was not his wife, as he had assumed. She stumbled through an apology and walked away awkwardly. The beauty of this mistake is that it served no purpose or gain whatsoever. Although, I guess he did get felt up.
Maybe it was a mistake to write this . . .