Fear of rejection is learned at a very young age. The single most dominant word in your early life was the word NO.
There is an expectation that if someone wants to do something for you, they will automatically volunteer. If you need or want to make a business or social change, individuals will naturally gather around and help.
I have found that it is easier to ask and accept an absolute potential NO. I have had a career of success in getting what I need to be done by asking.
I would like you to keep one other thing in mind. Always ask yourself what is in it for them. That answer will help you frame the question to increase your probability of getting a YES response.