Plateau in learning curve is caused due to:

Concept: In a learning curve (performance plotted against amount of practice), a "plateau" is a flat stretch where performance stops improving despite continued effort. Such plateaus are mainly caused by performance-limiting factors — conditions that suppress how a learner performs right now even though further improvement is still possible — the most common of these being physiological and mental fatigue built up over sustained practice.

Application: Among the listed causes, only fatigue behaves this way here: as practice continues without adequate rest, the accumulated tiredness temporarily masks the gains the learner has already made, producing the flat stretch on the curve. Once the learner rests and the fatigue clears, performance typically resumes climbing again — the classic signature of a fatigue-driven plateau.

Cross-check — why the other options do not fit:

• Maturation is age-linked biological readiness to learn a skill; a maturation gap limits or slows how much a learner can acquire at a given stage — it does not best explain an already-progressing learner stalling temporarily mid-practice.

• Motivation is a facilitating factor: rising motivation pushes the curve upward, so it explains continued progress, not a stall in progress.

• Interest, like motivation, drives learning forward when present; it accounts for sustained climbing on the curve, not for a flat stretch appearing despite continued effort.