It’s easier to learn the fundamentals before you’ve built up bad habits:
For example, when young children start working with music teachers, they start to work on simple music pieces. Easy music pieces of low to medium difficulty levels can be played with a wide range of playing styles, so there is no inherent need to acquire sound fundamental technique. However, when the students progress and attempt to master more advanced and difficult pieces that require higher speed and more expressive control, the quality of fundamental technique becomes the limiting factor for performance.
The music students with flawed fundamentals may at this point have reached a firm limit, unless they take off a year or two to focus on relearning the fundamentals correctly and then re-acquire the complex skills on that base.
Interestingly, recent investigations have observed neurological differences between students with flawed fundamentals and those possessing proper techniques (for a review, see Pascual-Leon, 2001). The importance of acquiring fundamental posture and movement patterns has also been demonstrated in some sports. For example, Law et al. (2007) found that world-class rhythmic gymnasts started their careers by studying classical ballet, a technically demanding form of dance, as children. In contrast, rhythmic gymnasts at the national level started with less structured dance activities, such as playful gymnastics.