You're not indulging the right perspective anon! Imagine being a runt in a country where most people don't even get close to 6' tall. Even in your twenties with puberty long behind you, you've got crippling phimosis that makes your 4.5" erection (on the best of days) incredibly uncomfortable, and enough people at your school knew about it that there's teasing and rumors!
Meanwhile, your 'little' sister grows like a weed, noticeably taller, stronger and curvier than almost every one of her female/futa friends.She's smarter, more driven than you- imagine the shame of hearing rumours about her and realizing that your 13-year old sister is bigger than you were- hell, bigger than you are.
Imagine wishing with all your heart; trying every stupid technique you can imagine to get it to grow, but you're stuck with a child's body while she shoots up in height- barely an inch shorter than you now and complaining about how she can't wear skirts anymore because her westerner-tier cock gets excited too easily with your new girlfriend is around...
(Who knows? By the time she's 21, she might be looking down on you instead!)