I lost in the Top 8 of a PPTQ today.
When I did, my opponent expressed his surprised that I had not won the turn prior to him. I had missed my chance.
The details are fairly boring. He only had one blocker, I had a bunch of creatures and the ability to pump a Walking Ballista. His only blocking option would leave him to take enough from the remaining attackers and the Walking Ballista. But I just drew my card, decided there was nothing I could do, and passed the turn.
Why? I had told myself I had already lost. There was a Ghalta out. A 12/12 trampler. I had no way to get rid of it. And I was so focused on the thing that I couldn't do anything about that I missed the thing I could do. Win.
And this is an important lesson from a costly mistake that I may make again someday. But I need to breathe and look at the situation. Not focus on staying in the game, but focus on winning the game. I didn't do that and I paid for it.