My Dad went to secondary school with John Lennon and was a couple years older than him. Dad was known for playing the drums and being quite musical and one day John asks him whether he'd like to be the drummer in a band he's forming. Dad was keen, but my Granny said he needed to prioritise studying and so he didn't join.
The band formed and were called The Quarrymen, and I think a guy called Colin was the drummer instead of Dad, who I believe was later replaced by Pete Best and then Ringo as they changed to The Silver Beatles, and then The Beatles.
I like to imagine that in an alternative universe my Dad said yes and that was history. I don't even mind that I wouldn't have been born if this had been the outcome – he really deserved to have had that lifetime.