8. SHOULD STATEMENTS: You try to motivate yourself with shoulds and shouldn’ts, as if you had to be whipped and punished before you could be expected to do anything. “Musts” and “oughts” are also offenders. The emotional consequence is guilt. When you direct should statements toward others, you feel anger, frustration , and resentment.
Source – one out of ten Cognitive Distortions from David D. Burns, MD, Feeling Good, Feeling Good Handbook.
See also http://feelinggood.com/