Because we're told not to by a parent figure.Sion_Barzahd said:
It's quite a common psychological method called Regression, where if we're told not to do something by an adult figure - especially if we're given reason to believe they are lying to us, we'll automatically rebel against it. GLADos uses a lot of these mental tricks like Passive-Aggression, Disassociation, Ego Assassination in order to create the Stockholm Syndrome in us. Especially as "we killed him in record time", which helps reinforce how BAD we are.
