Yeah, as filth said they work on their material for years until it comes to perfection.
As for inspiration, I never really have found that for tricks...I end up figuring them out on accident. I'll play around with cards, do something then gasp as I did something wrong that turned out to do something else that was good. Through this I've created an inversion effect, and a simple revelation (not the bottom card one).
One time...today I had created a move thanks to Brian Tudor whilst practicing the Rev. Five, not exactly inpspiration but a mistake led by someone else's work (this also happened with a sandwich routine I made though I wasn't practicing a trick to get it, it just resembled one).
Even though this, some people think of what they want to do and try to do it.
Whether its on accident or through commitment, its a trial and error process until it ends and you have a refined effect.
~PaCo