Distractions, task prioritization, loss of situational awareness, or disorientation.

Bottom line

Many airplane upsets occur while the pilot is engaged in some task that takes attention away from the flight instruments or outside references. When a pilot becomes task saturated, there is no awareness of input from various sources, so decisions may be made on incomplete information and the possibility of error increases. When a work overload situation exists, a pilot needs to stop, think, slow down, and prioritize.