“When combined with Kagan’s findings on high reactivity, this line of studies offers a very empowering lens through which to view your personality. Once you understand introversion and extroversion as preferences for certain levels of stimulation, you can begin consciously trying to situate yourself in environments favorable to your own personality—neither overstimulating nor understimulating, neither boring nor anxiety-making. You can organize your life in terms of what personality psychologists call “optimal levels of arousal” and what I call “sweet spots,” and by doing so feel more energetic and alive than before.”