Lessons
It can be challenging to learn an instrument. Music is a foreign language. Developing fluency in a language doesn't always come easily, especially since the grammar of music is entirely different than usage.
Even the most diligent student will develop bad habits, which can tragically prevent a student from progressing any further in her musical journey. THIS IS WHY so many students get "bored" with music and end up quitting. In reality, they aren't bored; they have stopped progressing in a meaningful way. A body that is misaligned or tense simply will not work the way it is designed to. Furthermore, most students are completely unaware of the source of their struggles, or that they are even struggling at all.
It takes time, patience, and a keen set of eyes and ears (i.e., an instructor) to develop a functional, dynamic posture and gorgeous tone.