"I began learning, long ago, that those who are happiest are those who do the most for others." This is not always true, we have to learn to take care of ourselves first, or we are unable to give what we want to others.
Stop asking yourself what if you can't do it, and instead as yourself what if you can? What if you can write a bestselling novel? What if you can accomplish your dream to be a published writer? If you're willing to work for it, you can.