I don't interpret it as having anything to do with introversion or introspection. You don't have to be either of these to have the desire and ability to sit qui

I don't interpret it as having anything to do with introversion or introspection. You don't have to be either of these to have the desire and ability to sit quietly from time to time (once a week/month). To me, the quotation draws a link between the ability to sit quietly and the condition of being at peace with one's self. Enjoying the mindful act of sitting quietly is a manifestation of such peace, and learning to sit quietly involves tackling ways in which you are not at such peace.