"I’m not sure who decided that three months was a magic number for accelerator programs." That's kind of funny to read. I never thought about it before, but I

"I’m not sure who decided that three months was a magic number for accelerator programs." That's kind of funny to read. I never thought about it before, but I suppose the others must not emphasize the origins of their features, which must in turn make them seem rather arbitrary. The 3 month duration comes from the fact that YC was originally meant to be a summer program for undergraduates (http://ycombinator.com/start.html http://ycombinator.com/start.html).