The sometimes crossed signals between testosterone and estrogen in the developing young body demonstrate the pliability of external gender. When that conflicts with inner gender indentity it can be quite traumatic, especially for 13 year-old boys. It may be a valuable right of passage for the heterosexual male if only for the simple demonstration that, like nipples, gender can be unpredictable and mutable. Only the effects of a handful of DNA and a few hormones separate the males from the females.
Even this doctor can shamelessly admit to having had peripubertal breast buds on the way to masculinity.