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.
Below are a list of tropes relating the different ways characters break
Willing Suspension of Disbelief by pulling a 180 and doing really weird, nonsenseical and/or stupid things. Why does this happen? Two reasons: the author sucks, and
drama requires them to.
NOTE: Since this is more index than trope, only
awesomely awful examples should be added, if at all.
Tropes