Personally, I have never faced such issues, because I am surrounded by very positive people who encourage any form of creativity. But for the unfortunate few who are often told that they are not good enough or their work is not worthy of attention- my advice is -keep an open mind for constructive criticism (very few will invest the energy, really), but don't give up on your passion(s).
Also, it is alright to feel frustrated or disappointed with your composition sometimes. But the important thing is not to quit. It may take months or years before you can create a masterpiece- maybe never (the worst possible scenario), but it is a lot better than not having tried.
And I have to include this interview of Vinod Khosla: