A patient with cerebellar damage can reach for a cup, and the hand oscillates around it before closing. Why does that specific pattern point to the cerebellum rather than to a motor or sensory problem?

A. Because the movement is produced and felt normally, only steered badly.

The symptom is diagnostic because of what it leaves intact: the movement happens and the hand is felt, so what has gone is the in-flight comparison. The patient falls back on a slower loop, notice the error, issue a fresh command, overshoot again. It is called intention tremor because it appears during purposeful movement and vanishes at rest, the opposite of Parkinson's.