Several studies have pointed out that fatigue (often called drowsiness) causes as many errors as being under the influence of alcohol. This should be pointed out to the roster managers in the airlines that appear to be using maximum hours limits as normal rostering hours.
IanW - Sleepiness. Fatigue - unable to suggest this as roster of F/O was short. He would have been peaking on this flight but that would be the case for any busy roster.
Limits - yes regretfully the world we live in these days. No use pointing at Roster Managers. NAA's, EASA, IACA etc