Write About What Fascinates and Electrifies

Per AdvicetoWriters, Warm Bodies author Isaac Marion advised:

Please don't write to appease others. Not the market, not a demographic, and not your family. Write the story that fascinates you in the way that electrifies you, and ignore everything else.

And I would add that writing about topics that "fascinates" and "electrifies" the writer will make writing, not easy, but a lot easier. 

And this advise extends beyond writing. For example, if you workout, not because you want to live a long and healthy life, but you hit the gym three times per week to be attractive to the opposite sex, you may come off as needy, which is not attractive.