What’s the cost of saying ‘yes’?
There will be a cost to everything additional thing you say “yes” to.
What do you have to give to say “yes” to the new thing? What new skills, resources, or assistance will you have to acquire? How much attention and energy gets diverted from something else, and is that something else more important? When you ask yourself this question, the answer might be that the cost is too high. If so, then your answer is a “no”, not “no problem.”