Don't Say No On Their Behalf
A friend has been a bachelor all his life. When I asked why he did not ask her dream out girl, he said she will turn him down. I agree that it is likely that she will turn him down, but it is also likely that she agrees to the invitation.
Don't say no on their behalf. This advice applies to me as well. Many times, I would say no on behalf of potential customers. They will say no to my appointment request. Say no to my offer etc. I wonder how many opportunities I have lost just because I said no on their behalf.
Even if the odd of getting a "no" is more than 50%. The cost of losing is negligeable. What we lose is a bruised ego, but we stand the gain something that we never have.
Say yes to yourself but not saying no on their behalf.