Chapter 20: Verse 121 (Partial)
Hayaa (modesty and shame) is something that every human being naturally possesses. One of the aspects of hayaa that is naturally found in mankind is the feeling to cover one's private parts. This characteristic can be seen clearly in the above example of Adam and Eve.
Like all natural characteristics, this quality may be nurtured and allowed to grow or it may be stunted to the point that the person completely loses this quality.
Beyond the natural feeling of hayaa, there can be an acquired aspect that is directly related to the strength of one's faith. This is the hayaa that comes about by realizing that Allah is always present and He sees everything that one does. There is no escape from Allah. When a person realizes this, he will be ashamed to perform any act that is displeasing to Allah.
Another helpful factor is for the person to think about all of the blessings that Allah has bestowed upon him. For example, if he really thinks about how great a blessing his eyesight is, he will be ashamed to use this blessing from Allah in ways that are displeasing to Him.
"Commentary on the Forty Hadith of al-Nawawi" - Jamaal al-Din M. Zarabozo, pp. 808, 809