Saying yes is good to the extent that you really want to say yes, assuming that yes is the best choice you can make. So, saying yes does not have to be a bad thing. So, in order to say no to one thing you must find other things to say yes to that will substitute those things. It is not about saying no to things you don't want to do but rather in focusing on saying yes to what you love and what believe in over mere emotional reaction to what happens to you in life.