Practicing the wrong way is like having a bad habit. The habit (practice) is bad but it locks in nonetheless.
Perfect Practice
To reach perfection, care has to be taking when practicing to encode things the right way. Good coaches accomplish this by:
1. Slowing down the action e.g. playing a piano or a violin at a painfully slow rate to make errors more noticeable
2. Chunking - breaking down the skill into smaller components and practicing these chunks separately. E.g. tearing music notes into pieces and practicing the notes separately
Books: Little Book of Talent, The Talent Code