You can't generalize on how people will behave. Even basic survival instincts are frequently (and humorously!) subverted in Real Life; and Hidden Depths or a Mysterious Past mean characters have a lot of leeway to act Out of Character. However... there are many things people are still unlikely to do, especially when previous characterization has given them some measure of an attribute in contradiction to their new behaviour. NOTE: Since this is more index than trope, only awesomely awful examples should be added, if at all.