Plateau in learning curve is caused due to

Performer hits a plateau in the learning curve when there is little or no improvement. The candidate may have reached limit of ability or become bored with task. Plateau happens in a learner due to variety of reasons vis-i-vis, not physically ready to improve, lacks ability to develop current skills, earlier incorrect learning, fatigue, moving from a simple skill to a complex skill, boredom, lack of motivation to improve, goals set too high, poor coaching/teaching.