Fatigue aside ... because as professional aviators, we should self assess and call in fatigued.

What if the pilot doesn't have the mental/emotional maturity to realize, that, although his/her job is, or can be for many, fun, he/she cannot forget his/her responsibility for the crew, aircraft, cargo, flying public and the general public?

What if the pilot sleeps on the job because of "Lazybastardism" ?