people don't change...

they just looked like they had.
the metaphor?

take a glass of water.
pour the water into another glass of water.
it's still the same glass of water.
freeze it, it still the same.
boil it, still that same water.

but try to make another guy tells if it's still the same water after the pouring and boiling and freezing without giving them any clue on what had happen.
most likely they'll say, "who cares? i still get to drink it."

:P