Tennis Myth :Keep your eye on the ball

Perhaps, the most often heard comment in a lesson is, “Keep your eye on the ball until it hits the strings”.
The simple answer is, no human has ever seen a ball hit the strings because
(1) the ball is on the strings approximately four milliseconds, and
(2) the human eye can’t record a four millisecond event.

A coach may have something else in mind when using this overused phrase. If you pretend as though you are watching the ball onto the strings, your head will remain still and will not hinder your swing pattern. Biomechanical studies have proven that the swing pattern lacks consistency when a player’s head makes a sudden shift during the striking phase. Thus, even though your brain may have sent down a signal for a perfect stroke, it may have also sent a message to shift your head, which will inevitably break down a well formed stroke pattern.

Source: SingaporeTennisAcademy.com