In Knocked Up, Seth Rogen is a goofy but loveable stoner who gets his one-night stand Alison pregnant. In 50/50, Seth Rogen is a goofy but loveable stoner whose best friend Adam gets cancer. His relationships with the two characters and their unexpected medical dilemmas unfold in a bizarrely similar fashion, because Seth Rogen has a very small yet specific range (involving beards and throaty chuckling).
4Seth Rogen Takes Them Shopping for Self-Help Books
Seth Rogen starts off trying to do the right thing (or at the very least, trying not to do the wrong thing). He happily takes time out from his busy schedule of smoking weed and doing absolutely nothing else and takes Alison/Adam shopping for self-help books so they can better cope with the baby/tumor growing inside them. This shows his compassion, because when your friends are going through troublingly uncertain times, the best thing to do is buy them books, rather than actually try to comfort them yourself.
However, before long ...