I think one of the major results of the psychology of decision making is that people's attitudes and feelings about losses and gains are really not symmetric. So we really feel more pain when we lose $10,000 than we feel pleasure when we get $10,000.
The idea that you can ask one question and it makes the point - well, that wasn't how psychology was done at the time.
The concept of loss aversion is certainly the most significant contribution of psychology to behavioral economics.