Eat Bitter

In Chinese it is call 吃苦chi ku。It is a core character building that teaches a person to achieve Gong Fu as a level of attainment rather than a practice.  Eat bitter is not a walk in the park, and it is not a self induced physical and psychological torture. Chi Ku is a test of endurance, diligence, patience, and willingness to go through difficulty to master an art.  It can come in many ways; one of the first tests of Eat Bitter comes in the form of zhan zhuang or standing meditation.  One starts slowly and builds up in time and endurance.  Many masters would not accept a student who was not willing to go through this basic training.
Chi Ku comes in the way of practicing a single skill thousands of times.  This is Chi Ku. This is Kung Fu.