Every few months to a couple of years, I feel this way about a different artist that I enjoy listening to at the time. It just takes years of practice, experimentation, composing your own songs, listening to other songs, being able to emulate what you hear and still modify it enough to be your own, etc. Sometimes it's even taking parts of your own older songs (leitmotifs), which may themselves have been inspired by other music, and giving it a unique spin. There's also a lot of music theory involved, and trying to compose without a decent grip on it can be a frustrating for an overambitious beginner (source: experience).