The person who remembers your last concern has kept the conversation alive.

Between two meetings, most people put you down and pick up their own lives. Someone who comes back to the thing you were worried about last time has been carrying a piece of you around in the interval, and the conversation you are having is not a new one but a continuation. That is rarer than it sounds, and it is felt immediately. Being remembered this way is a form of being taken seriously.

You can do this deliberately without it being calculated. After a conversation, note the one thing the person seemed most concerned about. Next time you speak, ask about it first, before your own news.