Saying no
The hardest part of saying no is facing the fear of loosing an opportunity or a person. It is an irrational fear, since no-one or no experience good for us is ever going to walk away and never come back simply because once or twice we said no from a place of alignment with our needs, and if they do, it means they were not right for us in that moment. What is worth for us awaits us. And the best thing of saying no except the peace that follows, is learning to do so gracefully, not offending anyone involved.