It's challenging to keep coming up with new ideas every day. It's an unsustainable venture. The mind will eventually buckle and demand rest. Imagination works in cycles. There are times when you rule the world and there are times when you're stuck in the desert. The key is to take advantage of peak creative activity.
When inspiration strikes, that's the best time to start planning. The ideas flow easily and you should ride it all the way to the end. If you don't, you will inevitably reach a stopping point, and you'll be wracking your head over a problem you could've solved from the start. You'll also never know when a new strike of inspiration will come, which can render your old strikes useless if you come up with something better. Basically, there should never be a situation in which you don't know what happens next.
Always be ready to ride the thunder. You'll never know when it'll strike.
