One of my most painful moments in poker came when I thought I’d mastered the beginner poker guide I was following. I had a flush on the turn and thought it was unbeatable, so I went all-in. One guy called, and the river brought him a full house. I lost everything. I realized then that no matter how good you think your hand is, there’s always a chance someone’s got something better. That one hand set me back more than just a few chips.