Desire to change the profession but the powers above say no

There are some tasks you lay ahead due to necessity, for example going to work, buying groceries, but there are some tasks that you commit yourself to out of desire ( shopping for a new pair of shoes or crafting a birthday card for a friend). What is the fine line between an obligation and a desire? How do you differentiate your sense of responsibility to your desire to help someone who has selflessly helped you? Does the feeling of obligation encroach into your desire? If so, is there a need to differentiate a sense of obligation from your sense of desire?

I was asked to write a paper that would benefit not only the pharmacy profession but myself and the clinic. Granted the paper would take much of my free time, researching, drafting, outlining, but I wanted to commit the time due to the aforementioned reasons. However when I approached my other colleagues, my commitment was interpreted as an obligation to the person who asked me to write the paper. True, the individual stands in an influential seat and has spent countless hours of non-work time to refer patients to my clinic, to advertise on my behalf and to promote and elevate my position to other colleagues. But my desire to write this paper was not out of obligation but from pure selfish desire! I want to write the paper DAMMIT but the forces above me have not granted me permission. *Sighs*