Good question. I don't know.
When I was little, like 7 or 8 I was terrified of anyone seeing me naked. I don't know why. My mother pointed out one day that she had seen me naked for a long time, but I was shy about it.
Then about the fifth grade, say 10 years old, my cock got a lot bigger than my classmates. Anything different with kids gets ridiculed. And they laughed and pointed at my cock. It is safe to say that almost no one knew what a cock was really for or why they got big, but I was humiliated for it.
All through high school, my cock was bigger than theirs. But we all had to shower together. And I got over the shyness. By collage, i liked to parade around naked, cock half hard swinging out in front if me.
I started looking for opportunities to get naked. As I went to the gym I would find a locker as far from the shower as I could and then walk to the communal showers and enjoy soaping and cleaning my cock. Nothing like hot water and soap to give a guy a hard on. Then slowly walk back to my locker. Towel over my shoulder.
It was an interesting journey from shy to flagrant.