I'm a big believer in "score effects." Give up an early goal -- or two -- and the way you and the opposition play changes dramatically; sometimes to the point that there isn't much more to learn from the game.
Liverpool made two huge errors in the first 12 minutes of Sunday's clash with Tottenham at Wembley and that was that. It wasn't just that they necessarily played into Spurs' hands because they had to get back into the game, it was the psychological damage done to the players on the pitch.
I don't like to bring up mental errors because I assume that you don't get to become a professional footballer -- and especially not a defender or midfielder -- without the ability to concentrate and execute during games, but it's hard to see this any other way.