The quote continues with " - a writer is a professional observer."

And she doesn't just mean the world right in front of you.  Although that is a great source of inspiration. Have you ever been stuck waiting somewhere and start making up stories with the people around you as characters? Giving them back stories? A reason for being there? A future?

Observing the world around you and asking questions? Why is she wearing that green bow in her hair?  Why is he so nervous?  Why are they not talking to each other? Trying to understand.

Do you have friends who can't fathom how you can write a story? Say they could never come up with an idea?  I'd bet they aren't watching the world around them. 

Is this you?  Do you pay attention to the world?