I don't think this means you shouldn't say no. It just means that you need to understand how to decide what to say no to. If your boss is the one who decides yo

I don't think this means you shouldn't say no. It just means that you need to understand how to decide what to say no to. If your boss is the one who decides your performance, and they would rather you dropped everything to help others than do what you're "supposed" to be doing, then you need to say no to what you're "supposed" to be doing. There is a bigger picture version of "saying no" in play here as well, though: is a company where your boss doesn't even seem to care about what you're "supposed" to be doing one that you want to work at? Will it make the best use of your talents?