Hot Tub Time Machine (2010)

Continuity mistake: When Lou and Nick are playing pool in the bar, Lou goes to break the rack and misses. When Nick goes to break them, the balls are racked in a different pattern. (00:50:10)

Adam: One little change has a ripple effect and it effects everything else. Like a butterfly floats its wings and Tokyo explodes or there's a tsunami, in like, you know, somewhere.
Jacob: Yes exactly. You step on the bug and the fucking internet is never invented.
Lou: Oh then you'll have to talk to girls with your mouth.
Jacob: Yeah. No. I was more concerned about bigger consequences like not being born.
Lou: Yeah. No. I don't care about that.

Trivia: When the foursome ski down the mountain and are looking around at the oddly dressed people, someone behind John Cusack says, "Hey Lane, you owe me two dollars". This was a nudge to John Cusack, who played Lane Meyers in "Better Off Dead" and was pursued in the snow by a crazed paper boy shouting "Two dollars!"

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?