1.) Stringing all those sentences together to make a novel is much harder than you think it is, especially if you don't do well with commitment and are not a self-starter. Falling into a diva rage (should you sell) upon seeing how an editor marks up your masterpiece will only complete your torturous demise.
2.) The near constant rejection is real. Depression, anxiety, and/or a penchant for overindulgence in alcohol, are often part of the author stereotype and stereotypes are stereotypes for a reason.
3.) Turns out, you DO need to know spelling, grammar, and all that English stuff from school. And quite a bit of math. And depending on your genre: science and history. Do not email your 10th grade English teacher and offer her apples to edit your novel. That ship has sailed, honey.
4.) Getting paid enough to live on is far more unlikely than likely.
5.) Differentiating between the 'voices in your head' being a psychotic thing and being an authorly thing can be a line as fine as frog hair.
BONUS: Sitting in the desk chair for hours on end is not cardio.