Out of curiosity, I always ask any TC/STC I fly with, what are the usual reasons for guys having trouble with command courses.
90% of the time, they say - task management, prioritization, complex MEL management, maintaining the sequence of the SOP's, and putting themselves under real or imagined time pressure. Mostly in the pre-takeoff phase.
All the things that are thrown out the window in 90% of the sim 'training' that we do.