When I was at Music school, I was told by alumni to say ‘yes’ to everything.
By ‘yes’ they meant every opportunity that came your way.
As much as it was well meaning, and endorsed the idea of ceasing certain moments, I think it to be equally, if not more important to know what to say no to.
Saying yes could compromise your integrity for a start and could take you down the road of selling out and being a hack that bares no resemblance to the adult you desired to be when you were a child. The second thing is that you can easily over commit yourself and burn out (I definitely do this from time to time).
Saying no means you are aware of what you have to offer and knowing when you are asked more than what you can offer. Saying no means you are thinking about what is important to you and whether saying yes to one thing sacrifices another more important thing.
Opportunities do come along, you can also make opportunities for yourself and sometimes we need to carefully consider the path we choose as to how we move forward.