We have the ability to extrovert or introvert because we can exercise these two functions. Most people can exercise these two functions at will. But as it turns out, not everyone can.
But introverting and extroverting are opposite functions. If we are extroverting then we are not introverting. And if we are introverting we are not extroverting.
Introverting is about bringing the energy close to our heart. Extroverting is about extending ourself to our outer realm. While introverting pull the circle around ourself closer. While extroverting we expand the circle to include things outside of us.
But know that ultimately we need to balance. One cannot introvert unlimitedly in the same way that one cannot extrovert unlimitedly.
Whether you extrovert or you introvert, the body will always seek an equilibrium. You cannot randomly extrovert to anything and everything all the time in the same way that you cannot introvert to anything and everything.
Most of us would not enjoy being forced to be in an orgy of drinking, drugs 24-7 (extraversion). And most of us would not enjoy being a monk that doesn't speak or interact with anyone 24-7 for months on end (introversion).
In expressing our unique individuality, we seek a balance between those two extremes. And what it means for the individual to do that means something different for every individual.
The body seems to have a sense of where and when that imbalance has been experienced. It experiences as a feeling of discomfort. Then it seeks to correct itself to try to achieve that whole again.
(Vipassana teaches us to correct our balance without experiencing a lot of aversion or craving. Experiencing and expressing these tends to start another wave that threatens to 'rock our boat' down the road.)