A student once asked me; "How come the music comes freely sometimes while other times I feel blocked and can't play?"
A perfectly valid question and one that many students of improvisation ask. You see, the problem is that many think they should be able to just sit down at the piano and play anytime anywhere. But this is unrealistic. Why? Because you can't force play!
Improvisation is play. And when you try to force the music to appear, the exact opposite happens. Blocks to receiving the music are set up and the spirit is let down. All this can be avoided if we learn that there is a certain ebb and flow to creativity. Respect this natural tendency. Learn to see the creative force as one that naturally goes away, only to come back again, stronger and revitalized!
There is a natural order to creating that, if respected and trusted, will serve you well. Listen to yourself and don't let your ego get the best of you.
Many students fear that if they can't go to the piano and play, they're creativity is dried up. Not true! They may be experiencing an ebb tide period. During this time, it's best to take a break from playing and come back later on when the creative waters return.