To determine whether you're an introvert or an extrovert, you must ask yourself one question: Where do you get your energy?
That's according to Susan Cain, best-selling author of "Quiet: The Power of Introverts in a World That Can't Stop Talking," and one of the most popular TED Talks speakers of all time with over 17 million views.
Imagine that you're at a party surrounded by people you like, she tells CNBC Make It. After a few hours of nonstop dancing and socializing, two things may happen. If you're an extrovert you will feel charged up and ready for the after party. Conversely, you'll leave feeling drained if you're an introvert.
"For an introvert, it doesn't matter how good a time you've been having and it doesn't matter how socially skilled you might be," says Cain. "At the end [of the party], your internal battery is probably draining and so you're starting to wish that you were home in your pajamas."
There's a biological explanation behind this: Introverts and extroverts have different nervous systems, says Cain, which means that each personality type reacts differently to outside stimuli.
Introverts, for example, react much more to stimulation than their counterparts. "For introverts, we feel at our most alive and switched on when things are a bit calmer because there's less stimulation coming at us," Cain explains.
On the other hand, extroverts' nervous systems react less to stimulation, which means that they feel at their best when there is more happening. "For you, the liability is that when there's not very much going on, you'll start to feel bored and sluggish," says Cain. "And it will be hard for you to stay engaged."