When you love people, the hardest thing is saying no. But it's so important to actually accomplishing your goals. So first you have to define (and refine) those goals. I find saying no difficult in all areas of my life. But if I say yes even half the time an opportunity presents itself, my yeses begin to mean less.
Saying no is easier when you can direct opportunity elsewhere. At my firm, we do this by steering opportunities that aren't right for us to others who can serve the need. Where a yes is appropriate.
Saying no sometimes requires distance. In both business and personal relationships charisma comes into play. And empathy. Some people are just difficult to say no to, and others pull at your heartstrings. Why wouldn't I say yes? That's when a no creates the space to think clearly.
Not saying yes or no is the easiest trap to fall into. I'll update when I'm more skilled at not getting caught there.