Nikolai is your classmate. He's not particularly popular. To be more precise, he is absolutely not popular. He is good at studying, but often skips and does not communicate with anyone. One day you stayed on duty with him and started a conversation. He was very friendly and seemed to you a cheerful, interesting conversationalist. It's been a couple of days, but he hasn't tried to start a conversation with you, or with anyone else. You don't understand why he's acting like this, so you try to start a conversation with him again