On Saturday, I played in a 4-round G/60 one-day event. I won all 4 games, 1st place, and sweet moolah. Overall, I was pleased with my performance.
However, no game came easily. Every position, even completely winning ones, can be botched.
In round 2, I spent 40 moves and 58 minutes to achieve a winning king and pawn ending. I triumphantly played c8=Q+ , and then my heart skipped a beat as he simply took the queen with his king. I had forgotten to protect the queening square with my own king! Fortunately, I had 2 extra pawns to win; however, they were rook and knight pawns, and if I had been missing either of them, it would have been instantly drawn.
I made mistakes, but my opponents made more mistakes. That is how chess games are won.