Okay, let me try this....momentum is like....a random number generator. Or the shuffle function on your ipod. We often notice that against all odds, consecutive numbers come up or the only 2 songs out of a thousand play back-to-back, something like that, right? Well that's how randomness works.
So with momentum, I believe when a few consecutive good or bad things happen to a team, they're affected by the perceived boost/slight in the corresponding way. Whether you chalk it up to "the gods" or "it's just not our day" or "it's our lucky day" - yes, the reaction to the seemingly unlikely series of events influences the reactionary behavior going forward.
ie - fumble recoveries are about a 50/50 thing. But when your team loses 3 fumbles in a game...a-it's rare to fumble that many times in the first place, and b-to lose 3 in a row is even more unlikely....your team may overcompensate or simply lose their edge, motivationally speaking. On the other hand, your team recovers 3 fumbles, you treat it like a gift from god and now have confidence, energy, and likely, a lead.
Believe me, I'm as big a stats guy as you'll find, but especially when it comes to these 20 year olds, momentum is a thing. It's in the same boat as letdown games. Whether it, in of itself, is a thing - the reaction to it makes it an actual thing.