Ideas don’t come when you need them, 

Ideas come when you note them. 

Ideas are like small kids. They keep talking to us all the time. They tell us things this and that; question us everything. If we talk them back, they get encouraged and think that what they are telling is important and talk more. But if we just stop listening to them, they gradually stop talking. They start thinking that its not important. That these ideas are useless. 
Therefore, I note down my ideas. And when I do so, more and more ideas come in. 

This also links to the “power of pen and paper” theory. Which says that when a thought is written on a paper, it becomes more powerful. 

We don’t know how all the ideas come from. Some say that an idea is just one of the successful permutations of all the facts, ideas and thoughts already present in our mind.

While some great scientists, philosophers, mathematicians, etc believed that all there ideas were told to them by GOD in there dreams or in prayers. 

Well, both may be right, or both may be wrong. In my personal opinion, an idea is a very small voice in our head that can bring big changes. 

Just very carefully listen to that voice, to bring change in your life. 

Keep talking!