Hot Tub Time Machine (2010)

Factual error: In the scene where they are watching "The Drive", the TV is not showing an NFL game at all. The field is 110 yards long. There is an overhead shot of the field and you can see two 50 yard lines and a C in the middle. They are watching a CFL game.

Adam: I vowed to master the chaos.
April: You have to embrace the chaos. You have to, that way life might just astonish you.

Trivia: Chevy Chase makes his first appearance; he farts. This goes back to the movie Spies Like Us when he is taking the test and he farts during the test, blaming it on the guy sitting next to him. The guy says, "Excuse me," as everyone looks at him.

Question: Considering that there are many different theories about how time travel works, such as the grandfather paradox, temporal paradox, etc., why did Adam assume that the butterfly effect was the primary rule of time traveling?