There is a fine line between envisioning success and daydreaming about it... The former is a motivator and a motor for your journey that you have to go through before you actually achieve your goals. The latter is a potential killer. It will kill your motivation, kill your need to actively pursue your dreams... Daydreaming is dangerous, as it takes you to the final destination, makes you feel like you're already there in your mind, even though you are just at the starting point in reality. It's a show-stopper and deal-breaker. How many things don't get done or even started just because one has already envisioned being at the top of the world and at the end of the journey, and eventually has decided not to go through the challenge and the ups and downs of the pursuit? How many times taking ourselves to the dreamy spot of achievement has discouraged us from taking upon a new task or coming out of whatever closet we have been sitting in (be it writing, singing, playing, painting, etc)... Daydreaming as in going ahead of oneself and not taking action while being happy with the dreamy end result, and fighting for success in real life, going through the (sometimes painful and long) process of realizing a plan of action are two dramatically different approaches.
Enjoy the pursuit. We are the people and we have a right to the pursuit of happiness, but how about also finding the "happiness in pursuit"?

PS. There is a book called "The Happiness of Pursuit". How to the point, and timely! Yes! More people should understand that there is happiness in pursuit, in learning, in achieving. That the process itself is almost equally important as the result (if not more?), that we can make it extremely positive for ourselves and learn from it even more. Curiosity is what keeps fueling our pursuits. Why not pair it with happiness?