Everyone who has ever taken a shower has had an idea.
It's the person who gets out of the shower, dries off, and does something about it that makes a difference.
-- Nolan Bushnell
If you try out your idea before, you understand that it is doing something about your idea that makes a great difference in your life!
If you have some good idea in the process of preparing for your examination/study, instead of shelving the idea for later time, take time out and test the idea out!
If you fail, you know the idea is good and not working the way you imagine, then you can take the next step to refine it or change it!
Act on and you will go one step nearer to your plan!