Don't be afraid to ask. Even if it's a stretch and you fully expect rejection, just ask. It's true that "the worst that can happen is they can say no." But what the old adage ignores is that "No" isn't merely a rejection; it comes with two important things: (1) knowledge of who you are and (2) how you think. Pitch a big idea to someone you didn't know before and, even if they initially say no, they just might come back to you one day because they know you and they like something about how you think. If you never ask, then you won't get an answer and you won't be on their radar.