The relationship between challenge and learning is not linear but follows an inverted U shape, where too much challenge can hinder learning, known as punishing difficulty. To facilitate learning, it is crucial to challenge the performer enough to make mistakes but not to the point of causing chaos. Practice difficulties should be in the optimal zone for learning, where there is some decline in performance but not excessively beyond that. It is recommended to aim for a 75 to 80% success rate in performance to strike the right balance between making errors for learning and maintaining motivation.