Practice does NOT make perfect - Scientists believe that striving to consistently repeat a physical action (like shooting a basketball free-throw or serving a tennis ball) is unnatural. Our bodies and brains are simply not designed to repeat the same motion in the same way over and over again. Variation invariably sneaks in, and the culprit for the inconsistency is the brain. It simply won't let you perform the same action in an identical way over and over again.

So the lesson is not to focus on the same physical action but the same outcome. Slight variations in form are a good thing and more natural to the body. Keep you eyes on the prize, not on perfect, repeatable form.
But I'm not sure how far we should take this. Clearly, practice does make perfect -- to a point. Beyond that point, it may not help or, at worst, get in the way of performance. Below are some notes & quotes from Practice does not make perfect - New Scientist

Note & Quotes

"The nervous system was not designed to do the same thing over and over again,"

Contrary to conventional wisdom that movement variability is caused by muscle activity, the Churchlandís team found that neural activity accounts for about half the variations.

Training muscles to perform a certain way through practice, such as countless hours teeing off or shooting a basketball, will not produce the same shot every time because the brain's behaviour is inconsistent.

After an initial training period, the monkeys' reach accuracy did not improve over time, suggesting that lots of practice can only improve movement control so much,

The researchers speculate that humans and animals evolved with this "improvisational style" in response to the predator-prey dynamic where predators never catch and kill prey in exactly the same conditions.

"Premium athletes' quest for consistency is a stark contrast to the way we evolved through history,"

Source - Practice does not make perfect - New Scientist

The Inner Game of Tennis by W. Timothy Gallwey