Thinking about Learning to say no, I think about when I was starting out as an actor. (Long side story, which I’m not getting into here – at least any time soon).
But something I was listening to gave me the advice, “Always be working.”
It didn’t matter if it was a volunteer role in an amateur production, or bit part on stage, or whatever! Just always be working.
And at the start of your career, it can be helpful (and also detrimental) to say yes to everything. Helpful because it can build up your network, bolster your reputation, and breed opportunities.
It can be detrimental, though, in that people may come to expect your extra effort or availability. They may see you later on refusing something, and maybe think that you’ve changed somehow.
A lot of it comes to balance.