As there are relatively few goals, anything that can turn a goal into not a goal or vice versa can have a massive impact on the game. For example the penalty decision against Croatia in the final.
Another thing that adds to the randomness is the chance that a key player may be sent off or injured.
To make that be specific -- in 44 of 64 games, and in every single penalty shoot-out, turning one goal into not a goal or vice-versa would've changed the outcome.
It is not so simple because goals in football are not independent from each other. A team that scores first has the opportunity to play more cautiously and go for more counter attacks.
