It can be hard not to doubt yourself at times. Most often late at night when editing or while reading a particularly good book. It's only human to feel that and wonder if what we are doing is worthwhile. Ask a writer why he does what he does and the answer will always be the same. We have no choice.
We might try to deny it, find other jobs or hobbies to fill our time, but none will ever give us that supreme joy of creating a story, and becoming lost within it. Nothing completes us in the same way writing does. Denying this will only lead to a soul sucking hole in your life that nothing can fill. Not even chocolate.
Even the greats have doubts. Stephen King's wife dug 'Carrie' out of the trash and convinced him to continue with it.
So late at night when doubt sidles up to you and whispers in your ear, remember he's been peddling those same wares for years. Don't buy into it.
Eat chocolate instead.