At different times I suspect any and all have been true. So I paid attention when someone taught me how to say "no" politely. I offer a genuine smile and say "Thank you for thinking of me. I am honored. However, my current commitments prevent me from being able to add this to my schedule." Then, if I can do so honestly I add, "You might ask Jane Doe if she might be able to help. She has the gift of (insert relevant gift or ability here)."
Really, I have lost fewer friends since I learned this.
Of course, sometimes I get a distinct feeling that God has an interest in what I am being asked to do and that is a matter of prayer and discernment. And sometimes I do something I'm not crazy about because I see it as a gift to someone I care about. But now I pay attention so I do NOT agree to a commitment without thinking seriously about my ability to meet that commitment, however small.
I am working to become more faithful in all matters. I believe this is pleasing to God and that my efforts are successful because God helps.