As a psychologist I always need to deal with the “say no” issue.
Say “no” to others is say “yes” to you. And there lies the trouble.
If you need “to be loved” by everyone, say “no” is hard. When you realize that this is just arrogance (after all: who is adored by everyone?) say yes to you starts to be a necessity.
And it is, is not human to say yes to everyone and everything because we are not toched by everyone and everything. Learn that rejection is a important part of life and a good thing in a way that helps relationships to structure themselves is the base to understand why to say no (or yes to you).