It doesn't just apply to marriage.
I was an absolute friggin genius till I started bothering having proper 'friends' and ****.
I basically did nothing for the first 13 years of my life and was described by every teacher as a genius, by every adult as a polite, happy, friendly child and by every kid as an annoyingly brilliant bastard.
Then BAM! Thirteen years old, I gets me some proper 'friends'. Start going out, getting drunk, going to parties and all of a sudden I'm a trouble-maker, a rogue, an abusive, violent, foul-mouthed, under-achieving little ****-head.
And sports! Sports will **** your head up no-end. Have you ever seen anyone truly brilliant who plays football? Hell no. Sure you get a few of those annoying all-rounder people who're good looking, intelligent and sporty, but they never really excel in any area and drift into a life of mediocrity.
The key to genius is unremitting hatred for all life. Love and excercise will **** you up.