To create is to act.
Creative thought is energy in action - it creates out of the unknown, unseen and unfelt and gives it a shape, size, number, flavor, fragrance. To create it in the mind is tough - but to really bring a fledgling, transient idea to reality - that is really enjoying the fruits of the enterprsie. To see the thought come to reality requires a sustained effort of the same creative action - with increasing focus and momentum.
In my experience, this is where a dream, an idea, a goal could fail - by losing steam in the making-it-come-to-reality phase. We do all the hard work of actually seeing what we desire, what we want to create. And when the time comes to actually experience it in reality, our creative energy deserts us. We see the goal and then we start seeing all-that-will-stop-the-goal from taking shape. We actively negate the creation with our doubts and fears.
As a result, the creative energy drops momentum rapidly and the dream goes back into being just a thought or at best a half-baked reality. That's not the outcome you envisioned. It's a sad end to it.
An exam, a performance, a desired business goal, happiness even - requires us to sustain creative energy through that bring-it-to-reality phase. I must stay with the thought and with this one question - how can I make this happen? These are creative thoughts and they need to be fed with more momentum by just being there, staying in that space, doodling, reading, planning in that direction (keep away from all that drives you in the other direction or some other direction). Write about it, draw it, see it for most parts of the day and the idea will adapt, will find ways to become a reality.
Many times when we create, we may have to exclude others from the process - just because they mess with the creative energy - simply because they are not tuned into your thought. The creative force or the vision gets diluted. (Think back into your own expeirence and you will know that most such decisions you took required you to step back into your own creative space and create it.)
But once you create the vision you wanted to, you become that, and then it is an experience that others share easily. So I suppose all one has to do is to stay with the creative process, Think of how-can-I-do-this and focus 80 - 100% of your thoughts consciously towards creating that. It should typically happen with so much creative energy going into it.
It's not as if it is all hunky dory. There will be issues. But you will find the energy and conviction to deal with it. You will also find the process energising. You will not lose sight of the outcome in your mind. Whenever challenged, the creative energy doubles up.
(If it does not, and drops off despite your best efforts, then maybe its not meant for you. You are unable to adapt to the final outcome. You have become larger than the goal. It's time to let go.)