Whenever you try to do something, whenever you want to succeed in something, whenever you want to make something work - assume you're going to fail.
Assume it's not going to work. Assume that the other person is going to say, "No." And assume that even if that person says, "Yes," or things seem to be going your away - assume that it's not going to pan out anyways.
I don't say this to get your hopes down. I say this so that you're prepared to extract the real value from the failure: the importance of learning, of adjusting, of adapting.
If you assume you'll fail, then you can ask yourself: "Why isn't this going to work? What's going to go wrong? What can I do now or next time to prevent this? Am I getting in my own way?"
Always prepare yourself for learning from defeat. Always extract at least one lesson from it. And try something else next time.
That is really how you grow.