Which primary psychological or physiological factor is considered most responsible for the formation of a learning plateau, and what condition does a 'convex curve' represent in the context of learning curves?

When there is a temporary halt or lack of apparent progress during learning, it is referred to as a plateau of learning. The major causes include fatigue, lack of motivation, complex subject matter, loss of interest, and unsuitable teaching methods. In learning curves, a convex curve represents a situation where the rate of learning is initially rapid and subsequently slows down with continued practice.