time

Have you ever noticed how all your best ideas come when you don't enough time to develop them? And when you eventually get some spare time to work on the ideas, they mysteriously disappear? 

I have found a way to overcome this. Creativity is like food or sex. You'd never say to somebody you desperately desire "I really want you so badly....how about Tuesday week at 3 o'clock?" or think to yourself "I'm starving! I must have some food later on!"

Similarly, there is only one perfect moment to develop your idea, and that is NOW.  So always be ready (in my case I carry a sketchbook everywhere)  to stop what you are doing and make as finished a version of your theme as is possible.  A scrap of paper and a pencil are all you need.  It's actually more fulfilling than sex because you have something to show at the end of it.

Believe me,  if you can master this you will be so happy.