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

Bottom line

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. Fatigue, stress, and work overload can cause a pilot to fixate on a single perceived important item and reduce an overall situational awareness of the flight. When a work overload situation exists, a pilot needs to stop, think, slow down, and prioritize.