Why is it that whenever I make a mistake trading, it always ends up being costly? I made a mistake this morning where I went long on a stock that I wasn't supposed to, and by the time I realized my error, I'd already lost over $6k on it. Why couldn't I have been $6k in the black by mistake instead? Fortunately I'm still up for the day, but I was ready to bang my head on the table when I originally noticed my error. Does this happen to anyone else? Is it just selective memory on my part? I would expect that all trading errors would eventually net out to zero, but it doesn't look to be that way at all.