Pooped

I'm pooped. Why do we say I am pooped when we are tired? If I translated that directly, I would be very messy. Anyway, I am really pooped. I was at work until almost 8 tonight. We had a machine demo at a Harmon's grocery store. In fact, I still have the machine in my car. I didn't want to take it back to work, I will in the morning. The guy I was going to have to let go quit today which made my life a lot easier. He got another job today that is going to work out well for him. I am grateful for small miracles. I am here yawning and I am pooped. Not messy, just really tired. It's a weird phrase: pooped.