Oh, my dude, who hasn't have this happen to them? I used to get mental whenever I lost an auction on eBay, or second guessed myself on an item for so long someone else bought it. I remember one time an item I wanted was snagged by someone else while I was clicking the "buy it now" button; and it also happened one time where I clicked "buy it now" and the item sold during checkout. I've had auctions for lots sell for a dollar or a few cents more than the amount I bid, or lost to someone who made a better offer than mine, simply got out-sniped, or I just literally fell asleep and missed an auction I was really invested in.
Nowadays if any of those examples I gave happen I no longer care. Sure, I get upset and shout a profanity or two, but by the end of those two, maybe three minutes of "rage", I just don't care. I've had a philosophy ever since I was a little kid that I try follow whenever possible, more so now that I'm older: one day I went to a KB Toys with my mother and I wanted a toy, but my mother was a bit strapped for cash, so she couldn't get me that toy, but she said she would next time, and while visibly upset given it was the only one left, I vividly remember looking at my mother and saying, "deal; if it's for me, it's going to be here next time we come". I remember hiding the toy and a week or so we went back, and there it was where I hid it, waiting for me because it was for me. Sure, you can argue the store had lousy employees who didn't attend to the store and what have you (although such wasn't the case), but you get my point. I honestly try my hardest not to get angry or have a fit whenever I don't get what I want. One door closes, and another opens, as they say.