Answer: Learned behaviour
Explanation: The learned behaviour is certainly the result of experience, that is, learning something through repetition multiple times. So, by repeating a certain act of looking at a sticky note, Richard began to think of clue that leads to password, and then only thinking of clue could remember password, which is a learned behaviour. This learning can also lead to a permanent change in behaviour or at least a potential change in behaviour, because any learning, even a simple clue, to getting to the password changes the way people perceive their environment and behaviour.