Write what you know. Is that good advice?

I was working on an article tonight and had to do some research to verify some information. Suddenly a phrase popped into my thoughts.

Write what you know.

I'd heard that advice in high school; heard it again in college; heard it once or twice during my graduate studies; read it on the web.

Now I'm wondering, should I be writing about this particular subject?

"Wait a minute," this voice in my head said. "If you write only about what you know, why do you need an imagination?"

Think about it.

Did Lewis Carroll know about what it was like to fall down a rabbit hole?

Did Clement Clarke Moore actually have to meet Santa Claus to describe him so endearingly? 

How many vampires did Bram Stoker run into before he created Dracula?

How much science fiction and fantasy would we enjoy if we had to know everything about other worlds?

See where I'm going with this?

Now, if I have a character who is undergoing a surgical procedure, I would have to do a lot of research to get the procedures accurately on the page. I still wouldn't know how to perform them but I'd could write about them.

I guess if you're writing a memoir, it's best to know what you write, or at least write about what you THINK you know.

So to all those people who told me, who told you, I say go ahead, fall down a rabbit hole before you pen your version of Alice's Adventures in Wonderland, but make sure you're female because otherwise ...