How boring is that. I mean, what do most people know: school, work, traffic, grocery stores. Ho Hum. I can see you yawning already.
Is writing only to be the domain of people who live exciting lives?
Must my characters be doomed to never travel the world simply because I can't afford air fare to any exotic places?
Because I say turn that saying on it's head. Don't think of it as "Write what you know." But instead as "Know what you write about."
You want to write about Paris in the Spring but have never been there? Check what time the sun rises and sets, check which flowers are in bloom, check what time the different attractions open, and if there is a fee for them.
You want to have your characters play Scrabble or chess or even checkers. Make sure to look at the game board and the directions. You may think it's not a big deal if you make up the points a certain word earns, or the move a chess player makes, but chances are someone, somewhere, who reads your story will know if you're making your characters do something that's not possible, and will lose faith in your story because of it.
If you can actually do the thing or go to the place, even better. But sometimes that's not possible, so the next best thing is research. And the internet is a wonderful source of all kinds of information.
So, you don't have to limit yourself to only writing about what you know, but if you are going to write about something, be sure you learn about it first!