In doing so, he elucidated many issues with simplistic notions of rational choice: endogenous preference formation (certain actions today can change preferences tomorrow, so how does one decide which preferences one prefers?), framing (people express different preferences when the same question is asked different ways), imperfect rationality (weakness of the will, emotion, impulsiveness, habit, self-deception) and our adjustments for it, and time preferences, among others.