Fatigue is frequently considered as one of the influential factors for aviation safety. Pilots and aviation technicians are likely to suffer from fatigue. The technicians are responsiblefor aircraft maintenance. This article is intended to explore some studies about fatigue. This article tries to find the clear definitions of fatigue, its causes, its clear indicators, and its influence to psychological aspects related to performance failure especially pilots’ performance failure. The article is closed with some tips to avoid the performance failure due tofatigue and some tips to overcome fatigue.