I shall reinforce what Bernhard has said because I think this principle is important enough to have application in composition, improvisation and areas of life unconnected with music for that matter.
There must be some sort of discipline, even in regions commonly thought to be the preserve of "inspiration". The real benefits of establishing a discipline come later in life. If you keep working over the years, it becomes such an enjoyable habit that you rarely experience "off days" or laziness anyway.
Admittedly this is probably easy for me to say because music has never given me a bad moment and I honestly cannot remember many times when I "couldn't be bothered". I may sometimes be lazy in the specific but rarely in the general. Nevertheless I have found that the quality of output was often grossly uncorrelated to the emotional impetus which gave rise to it.
My reactions to my own music are markedly variable. Sometimes I think, "Wow, that's good !" and then the next day, the next time I hear it, "That sounds a bit slack. I shan't try that way again." I have learned to take delight in the ordinary as well as the extraordinary. Indeed, the older I get the more important this discipline and delight in the ordinary is getting.
Then every now and then, something extraordinary does occur and I realise that saying about the Buddha being the hedge at the bottom of the garden is quite true. Discipline and serendipity - two parts of the one thing.