The Poke Choke.
The Pokes should have gone for 2 at the end of the 1st OT. Instead, they kicked the PAT and sent it into the 2nd OT, where TCU had the tactical advantage.
That's the same sort of calculation that Lincoln Riley made against Georgia in the Rose Bowl. In the 1st OT, with UGA having kicked a FG, facing short 4th and goal, he decided to kick for the tie instead of going for the TD and the win.
That sort of thinking seems to bite you more often than not.