If you haven’t reduced down to three choices, you haven’t understood the question/task well enough to identify the first three choices.
Many of them come down to:
Unable (willing or not, this is more obvious though if willingness is there)
Doing – choosing
So the first step with any problem is to understand it well enough to figure out which of those three applies. And often once you do you can either:
Set a boundary (be assertive): I will not.
Set a boundary and ask for help: I am unable without support, and I am willing to explore options.
Confirm and agree: If I’m understanding, this is what you want me to do, and if that is correct, I am willing and believe I am able to do so.