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Part of it is just genetic.  The other part is that hand size is determined by things like body hormones and how much you use them.  If you don't ever lift weights or try to stregthen your hands then they will always be weak. 

But i gather that you probably don't care about the mechanics of your question....... so have you ever heard of Stoicism?  There was once this roman emporer that wrote a book for himself to help him get through life by remind him of the traps that he always fell into.  He'd sometimes worry about inconsequential things, like we all do, that only detracted from his life.  And he'd write several entries and then sometimes would go back and review the insights that he had so that these lessons weren't lost.  Stoicism may be something that you'd be interested in, a lot of the people into that are pretty literate or into philosophy in general.  It helps them not be worried by life when it gets too harsh.  Btw, that guys book is called Meditations and its very popular now even though he never meant for others to have read it.  

Same for me, shoe size 13 since age 12. Worse, my left foot is actually a full size longer than my right foot, making it very difficult to find a pair that fits well on both. The slang for such big feet here is "steamboats" (lux.: Dampschëffer), but I always replied they're Titanics instead

Spoiler!

because they don't allow me to walk on water

I'm 6'3", so it's not that obvious for me, but my grandfather had it much worse. He had shoe size 12.5 (at a time where such big feet very much rarer than nowadays) but was only 5'4", so everybody around him joked he looked like a clown with oversized shoes. At yet he never let it affect him and was the kindest person I ever knew.

playing piano will make your hands skinny. It did for me at least.

But I'm not a teen anymore, my fingers won't become longer and that's the main issue for me. My middle finger is 8 cm, pointing finger is barely 7 cm long and they are also very thin compared even to teens and women