When I Say No, I Feel Guilty: How to Cope - Using the Skills of Systematic Assertive Therapy
Manuel J. Smith
The best-seller that helps you say: I just said 'no' and I don't feel guilty! Are you letting your kids get away with murder? Are you allowing your mother-in-law to impose her will on you? Are you embarrassed by praise or crushed by criticism? Are you having trouble coping with people? Learn the answers in When I Say No, I Feel Guilty, the best-seller with revolutionary new techniques for getting your own way.
"What is the book that changed your life? (not novels or religious texts)"
I think it's a wonderful way to connect in a less superficial way and learn a little more about each other. It's also a wonderful way to discover new books worth reading.
This is one of them. The full list is here.