Sky

1. You will end up on a terrorist watch list.
Unless you are a romance or literary fiction writer (and even then, only some subgenres of these), you will be researching things that look very suspicious to the outside observer. You will be looking up explosions, murder, diseases, and a great variety of things that the government will find very perturbing. You will have "how to get bloodstains out of anything" and "how to carry concealed weapons" bookmarked on your browser. This is inevitable.

2. You will learn things you did not want to know.
Whether it be the exact nature of the rotting process, obscure sexual positions that hurt to think about, types of scarring, true horror stories, or an in-depth study of BDSM, you will learn things you really wish you hadn't. Even if you are looking up something that shouldn't have these results, you will somehow find your way to a link to something that will never leave your mind. Ever. You have been warned.

3. You will be rejected. Over. And over. And over.
It doesn't matter if you are JK Rowling (who, by the by, was rejected by lots of people). You will be rejected. You will be rejected by so many people you won't think you can find someone left who can even look at your manuscript. This will happen. It is inevitable.

4. You will develop sleeping schedules inconducive to sanity and/or human life.
You will discover that your best time for writing is at some ungodly hour that no one thinks to be awake at. It will either be very early in the morning, very late at night, or at some strange midpoint between the two. If, by any chance, you find a remotely diurnal writing time, it will be in the middle of Other Important Things.

5. You will find yourself performing eccentric activities.
One day, you will drive 5 miles out of your way to pick up pens at the local gas station. You will jump out of your shower, dripping wet, just to scribble something down on a notepad. You will burn dinners, because that annoying beeping sound is nowhere near as important as this scene you're al... most... done... with...
You will find yourself staring inappropriately at people who you feel would make good character models. Somewhere in the middle of a perfectly ordinary dinner conversation, you will blithely mention some little tidbit from Rule 2 that, as it turns out, no one else wanted to know, either.

6. You will begin to speak of your characters as if they are real people.
This will confuse those who do not write. Those who do write will understand.