Q: And if yes how do you manage to do so?
A: first, i must figure out whether the 'idea' is supposed to be the beginning of the song, or not the beginning. if it's the beginning, then just run through it in real time and then have more ideas while already in the song. if the idea is the middle, this is much more difficult because then you have to figure out what came before, which is like writing backwards. which for me is almost impossible. but i have developed some tricks for this, such as asking a trillion questions, trying 100 things, or, seeing what comes AFTER, and then continue from there and hope that somewhere along the line a beginning reveals itself in some kind of cyclical construct