That is a common expression in English. It is similar to "I know I'm preaching to the choir". It's said when you are assuming that they understand what you are telling them. I don't want to go to work tomorrow--you know how it is! I don't want to show weakness in front of my friends--you know how it is.

It suggests that the speaker assumes the listener can relate to the situation, clearing out the fridge before Thanksgiving is something many people do to make room for all the holiday food. It's a way of reinforcing a sense of familiarity and connection.