Every (good) coach will encourage you to set your aim high and strive for the things that you're not quite sure are possible. After all, that's one major aspect of our job. We are here to guide and push you to do things that we know you're capable of - even if you don't.
But, it's also important to keep your expectations realistic. Often times, high-drive individuals look to accomplish remarkable tasks in an even more remarkable time frame. Sometimes it works out and good things happen. Other times, you are met with the cold, hard truth that it's just not going to happen like you thought it would.
This brings to mind one of my favorite quotes:
"Everybody's got a plan 'til they get punched in the mouth." -- Mike Tyson
It's a tricky line to walk. Staying realistic, but yet shooting for the stars. I don't claim to have the cure-all for this. I'm merely suggesting that you monitor this balance when you find yourself having success, as well as when you are met with disappointment. These two occurrences are simply opportunities to check-in with yourself and ask the big questions.
Like most topics covered on this blog, it really all just boils down to being conscious to what's going on and then making the appropriate adjustments on fly so that you maintain positive momentum OR slowing negative momentum in an effort to turn the tide.
In either case, consciousness is the key. After that, it's all just work.