It stings when a friend tells you no. Respecting it anyway is how they know they can be honest with you.

A refusal from a friend is a sign the friendship is honest. It stings, and the sting is worth taking, because a person who cannot say no to you will eventually lie instead, or quietly resent the things they agreed to. Accepting a no without a campaign is how they learn that honesty is safe with you. That is also what makes their yes mean something.

When somebody declines, say fine and let it go without a second attempt. Do not go cold afterwards, since that is a punishment they will feel. Make sure your own no is available for the same reason.