Crediting retired developmental psychologist Jerome Kagan, Quiet recognizes that there is not a single cause for a given behavior; there are many routes to behaviors such as being slow to warm up, shyness, and impulsivity.
Mengutip psikolog pengembangan diri Jerome Kagan, Quiet mengakui bahwa tidak ada penyebab tunggal untuk perilaku semacam itu, melainkan ada banyak sebab munculnya sejumlah perilaku seperti kurang bersemangat, malu, dan impulsif.