How hard (or easy) is it to find a career that EXACTLY fits your personality?

[sapphire_wisdom]

I'm hoping to get in to the field of health social work. But do not know what career to choose. I have a strong desire to promote healthy behavior,learn about diseases and basically help people. So I'm thinking of getting a joint MSc on Public health(health promotion) and Social work. But I also like to posses knowledge about the treatment part of diseases also. For instance I would like to know how and why cetain diseases occur and how to treat them. Does Health promotion cover all these areas? If not do I go ahead with my chosen area and do my best? or will I be unhappy not doing EVERYTHING that I like to do?