In meditation they say that one must be wary of ambition. Sitting is not about achieving anything. Sitting is about sitting. Similarly with writing or practicing music, I feel that one must approach the activity with a mind at ease, without any pre-conceived notions of achieving some goal. Only then is there space for the juicy feelings and thoughts to bubble up organically and spill out onto the page. Only then is the mind and body relaxed enough to settle into focused exercise.
Another precaution I've heard in meditation is against mental rejoicing at having achieved some new level of awareness or skill. This is folly because in that moment of patting-myself-on-the-back, not only do I reinforcing my already-inflated ego, but I actually lose concentration and forfeit whatever advanced mental state I was so excited to have achieved.
Beware the Big Breakthrough. Beware any notion of "NOW, that I've achieved this thing, everything will be different." It's a very exciting thought to have, for sure, and it's one that is a frequent visitor to my practice temple. One morning, I'll be practicing some novel way to accompany myself while I sing. After some time passes, the physical motion becomes easier and my body and mind relax into the groove. I feel elated—as if I'm on the verge of some great discovery. All of a sudden, my conscious, commenting mind, recognizes this feeling and rewards itself: "Yes! I've made a big breakthrough and now I will finally be able to perform that solo piano show I've always dreamed of."
You can see where this is leading. Not only have I still not performed that solo piano show, but also I probably didn't continue to practice whatever exercise I was working on for much longer. I lost that opportunity to connect with a continuity of practice. Lasting progress does not come in giant leaps forward but in steady commitment to doing the same thing over and over again.
This gets to a deeper truth about practicing and brings me back to where I started. Practice that is motivated on achievement of some lofty goal engenders these sorts of dangerous habits. Such is a well-accepted tenet: practice must be done for practice's sake alone. I would add that practice must be enjoyed for practices sake alone. After all, it is our enjoyment or interest in the present moment that constitutes true freedom.