The greatest joy that I have in this life is helping others.  Whether it's been assisting a family to find their forever home, guiding a new realtor to build a successful career or introducing someone to a product that has benefited thousands of others that maybe they've never heard of before.  Whoever told you that you have to choose one thing to do and only do that suffers greatly from limiting beliefs.  How about you choose a guiding principal and then build on that instead?