I think this is a normal occurrence in the creative process. More importantly, I think it is an essential aspect of the creative process. If a composer were to like everything s/he created, chances are that composer would be not a very discerning individual, and their music would likely reflect that.
One of the skills that I think composers need to develop is discernment; the ability to evaluate whether idea y is worth pursuing or not.
The difficulty for most student composers, as I have mentioned before, is that their level of musical sophistication exceeds their level of compositional technique.
Why? At Memorial University (where I teach), most students don't start formal training in composition until their fourth semester, by which point they have spent years developing performance skills and, once they are in university, learning music theory and being exposed to at least some "great" music (I realize that greatness is a potentially problematic term, but perhaps I will discuss the use of this term in a later post). By the time that most students are just starting their compositional training, they already have a pretty good idea of what they like and don't like in music, which, when applied to their own compositions, results in the phenomenon of knowing that a piece, section, or musical idea is not as good as they would like it to be, but not knowing exactly how to go about improving it.
The solution I typically recommend is to push forward with your musical ideas as best you can, even if you are not convinced of their quality, because it is often only by doing this this you discover the potential of ideas to grow into something bigger or different, or at least something to which you can feel more attached. I consider that part of my job as a composition professor is to suggest strategies for building on their compositional ideas in order to grow/transform them into something they like better.
It doesn't mean you necessarily keep and develop every musical idea you ever come up with; it just means that you often need to work with an idea for a while until you come to a better understanding of what it can develop into.
Should you ever discard your musical ideas?
I don't think so. For two reasons:
- If you have worked very hard on a musical idea, there is a good chance that it has value.
- You don't have to use it right away. You may find a use for it later, possibly in a different section of the same piece, or possibly in a different composition. You also may never find a use for it, but since we don't know whether we will eventually find a place for it or not, it makes sense to keep the idea, but just set it aside for now if you don't feel it works in the particular section of your composition for which it was originally intended.
- There is no reason to throw anything away, even if you are convinced that it is garbage! Notation files on computers use very little disk-storage space; instead of dumping a file in the trash, just put it in a compositional scraps folder because you never know if the idea might evolve into a useful idea in a different piece.