Your friend will tend to overestimate your abilities and your resources, and you'll probably get swept up in their grand visions. They'll talk you up, whip you into an excited frenzy -- and then you'll both find out, sometimes too late, that you can't really accomplish what you thought you could. You'll spark up each other's competitive sides, though, and you'll want to take on big projects, even when that's not the best idea.
This will come from a good place, in the sense that it will result from a feeling of positivity, optimism and expansiveness. But your beliefs and ambitions might not match up as well as you'll think they do in the beginning of your friendship, and after a while, it'll become apparent that you're working at cross-purposes. It could come as a surprise when you think you've been working in tandem but find out that in fact, your efforts have been going directly against each other. As usual, compromise and making an effort to really listen to each other will help a lot.