Nothing. Or everything.
As the Good Will Hunting guys prepare to reunite for a biopic about mobster Whitey Bulger, here's a look at how five other pairs of actor dudes fared when they rekindled their big-screen bromances:
1. Robert De Niro and Al Pacino: Heat was classic! Righteous Kill, released 13 years later, was, well, an "embarrassment," per the critics. So, yes, the nightmare scenario for Matt and Ben 2.0.
2. Clint Eastwood and Morgan Freeman: So, the first time they shared the screen, in the Eastwood-directed Unforgiven, Eastwood won two Oscars. The next time, they hooked up, 12 years later in the Eastwood-directed Million Dollar Baby, Eastwood won another two Oscars, and Freeman won his first. So, yes, this is pretty much the dream scenario for Matt and Ben 2.0.
3. Vince Vaughn and Jon Favreau: Neither was exactly hot or fresh from Swingers when the stars reteamed in 2001's Made, a gangster comedy written and directed by Favreau. The movie grossed a little more than Swingers did at the box office, but was in no way more money than its predecessor. The lesson here for Damon and Affleck? In case the Bulger thing goes bust, don't break up the team for good—just start trading lines in a string of hit romantic comedies, a la Couples Retreat, The Break-Up and more.
4. Paul Newman and Robert Redford: The gold standard for guy teams (non-sequel divison, natch). Their attempt to replicate the chemistry of the western Butch Cassidy and the Sundance Kid in ragtime-era caper The Sting wasn't just successful, it was wildly successful. Can Damon and Affleck find the formula? Newman and Redford couldn't—for decades after The Sting, the two waited and waited for the next great team-up project to come along. It never did. Newman died in 2008.
5. Jack Lemmon and Walter Matthau: If Matt and Ben are very, very good, and get along very, very well, then they, too, can make like this classic duo, and use the Bulger biopic as a jumping off point to make movie after movie after movie until they're both grumpy, old you-know-whats.