I remember at Junior Country Cup one year, i had a classic game about 2nd last game for the tournament.
It was one of those games as a youngster where you open the first few frames and you lose all confidence. Every spare seemed more impossible as the game went on, so much so that nearing the end of the game, my team manager declared that if i didn't close the next frame, i was walking home!
Needless to say i closed the next two frames, walked away with a nice 103 game, and a place on the team bus home!
Somehow i actually still got a game in the last, and won my point, feeling like i couldn't miss a spare all game.
Momentum is certainly a powerful friend/foe...