I've definitely had my share of "oops" moments. Like this one time, I placed a bet on a basketball game, not realizing the team's leading scorer was out due to injury. I was so sure of my bet until the game started and the announcers mentioned the injury. It was a forehead-slap moment, but it taught me to always check the latest team news before placing a bet 
Those are the kind of things that can happen to anyone, I remember that something similar happened to me once when playing poker, I took a look at my cards and I had an Ace and a King, and in the community cards there were two Aces and a King, so I had a full house and I was pretty use I had my competitor beat, however when it came the time to the showdown I realized to my dismay that I had an Ace and a Jack, needless to say I lost the hand and some money by that mistake.