My theory is this - obviously they are closely matched. Losing in the 12th game would make Caruana very hungry to come back again and again. Now, consider what

My theory is this - obviously they are closely matched. Losing in the 12th game would make Caruana very hungry to come back again and again. Now, consider what happens if Carlsen crushes Caruana in the rapid or blitz rounds - this sends the message "you will never beat me at rapid or blitz, and no amount of preparation will save you". Caruana will never forget this. This will be in his his head the next time they play, and the pressure to avoid the tiebreaker rounds will be huge.