I am currently reading this essay turned book by Elle Luna. With her colourful illustrations, she challenges the reader to think about what they have in their life - a job ("something typically done from 9 to 5 for pay"), a career ("system of advancements and promotions where rewards are used to optimise behaviour") or a calling ("something we feel compelled to do regardless of fame or fortune"). I wouldn't do the book justice by describing it, so I'll share a passage where Elle writes about the difference between should and must.
Elle on must:
If you haven't read the essay that inspired it all, do yourself a favour, read it now (then go read the book!).