Both powerful words
Say YES to any opportunity that has your own best interest, has the potential to help others and is with alignment to your goals.
Say NO when there's a demand on your time that doesn't light you up or inspire you to become a better version of yourself, or doesn't give energy back to you, in any form.
Both words have their own power
And you can, and are encouraged, to use them both equally, without the need of explaining yourself.