They feel tired when they have to deal with many people.

Many people think that an introvert is shy and cannot socialize. In fact, not all introverts are like that. They can easily mingle and interact if they have to, even attending events where they meet lots of people. But just because someone comes to a party doesn't mean they like it, right? An introvert doesn't mind meeting and interacting with many people, but that doesn't mean he likes it. One of the unique things about introverts is that they feel tired very easily when dealing with many people, so they can never last long at a big event. Even if introverts seem fine on the outside, they're actually tired of having to meet everyone, chat, and pretend to be interested in any topic of conversation that comes up.