The American Name Way

What's the deal with people who are named john going by jack, like jf k or jack ryan? Or am i crazy? Isn't it acceptable for jack to be a shorthand for john, it's the same amount of letters? I feel like that is something, tha, i've never fully understood that american name way thing, weryou. Ye, i mean, if rip taylor was still alive, you could do him tooye throwing confetty,. Te that'll be our answer.