> One person will have crashes and problems all the time, and the other person, smooth sailing. Nobody knows why.

http://www.catb.org/jargon/html/Q/quantum-bogodynamics.html

In all seriousness, it probably has to do in large part with gestures broadly global state. Registry, configuration, what else is running on the system, how up to date it is. There are so many possible different settings, parameters, processes doing weird api calls, that it's a combinatoric explosion.