You'll tend to see your friend as impractical and overly optimistic, and you won't hesitate to express this. As your friendship develops, this could become a real problem. Whenever your buddy has a brilliant idea, you'll quickly yank them back to reality, exposing the flaws in their logic and the practical reasons why the idea just won't work.
You'll think you're helping them, and you may be right -- they could be a real dreamer. But dreams, hope, faith, inspiration -- all of these are essential complements to reality, practicality and sober thinking, and your insistence on the latter will make your buddy feel inhibited. It will be as if you zap the life and energy out of every good idea they have, and they'll grow tired of it. You could even impede them from reaching their goals, simply by making them feel defeated, though that's the opposite of your intention. You'll both have to learn to live with the other's perspective.