A brief encounter can leave a tone that lasts beyond its facts.

You forget the content and keep the tone. A two-minute exchange at a counter is gone from memory by lunchtime, while the feeling it produced is still colouring the afternoon and attaching itself to things that had nothing to do with it. That is why manner matters more than accuracy in small dealings. Nobody remembers what you said to them; everyone remembers roughly how it felt.

With the brief encounters in your day, pay attention to what you leave behind rather than only to what you get done. And when your own mood turns for no clear reason, check whether something small set it.