Your co-worker shuffles in at around 9:45 a.m., eyes averted, and makes a beeline for the coffee pot. Although your colleague may not verbalize his current state of mind, his mug — “Don’t talk to me until I’ve had my coffee and then after that still please don’t talk to me,” it says — informs you of it.

You, being a morning person, just don’t understand this grumpiness. You’re all chimed up and ready for pleasant chitchat. “Good morning! How are you? I’ve already run five miles, and then I sent you 10 things to do. Let’s meet to discuss them in five minutes.”

Your colleague looks at you with a stare that says, What about my nonverbal cues or my coffee mug made you think that I would ever want to talk to you at all, much less in the next five minutes?

Fast-forward seven hours. It’s about 4:45 p.m. Your brain is mush. Your once reticent co-worker bounds into your office brimming with enthusiasm, ready to discuss what’s on his mind and execute right here, right now. You look at him with a glassy stare that says, I have no brain cells left. I am hungry. I just want to zone out until I leave. Stop talking to me, and I wish there was a mug to explain my late-afternoon brain fog.