Envisioning, dreaming and imagining could be grouped under the same category. I believe humans by nature dream and visualize certain things they want, their imagination takes them there without even trying, especially if they want something badly.
The hard part isn't envisioning, the hard part is the strong belief in the dream even when the current situation doesn't seem promising, that's where things could get blurry.
Let's say you want a certain job, or a certain house, and you keep thinking about it and your mind just keeps envisioning you having it but everything that's in the present doesn't seem to lead to it, most people would give up on it, because they may be short-sighted,may not believe enough in themselves to have it, or may not feel deserving enough.
That's when self-belief comes in, if you believe in yourself, and you stay persistent, that dream will come true, you will naturally start doing everything you can to have it.
Accept and be grateful with whatever you have but keep working towards what you really want.
Just always remember that anything worth having, doesn't come easy.