It's worth noting that a really good model (or the betting line) gets the predicted margin wrong by 27 points per game on average. That's four and a half goals! And upsets are very common, occurring once every three or four games.
But correctly picking upsets is super difficult. At least in betting, when you tip an upset you get an oversized reward, which makes it worth doing more often. In a tipping comp, you get 1 tip no matter how unlikely it was. So you need to be smart or lucky, or both.
Of course, the person who wins the comp is always a contrarian, because that's what distinguishes them from the pack, but most contrarians will do worse than average.
So I'm tipping an upset every time the line is <13.5 points after this post.