The nurture part deals with reinforcing the valued traits and putting a lid on the less desireable behaviours.
With so many parents abdicating their role in favor of daycare or other surrogates (at best), it should be no wonder the results are jumbled.
The whole argument was old when Mark Twain wrote Puddin'head Wilson.
Then, too, some folks just ain't wired right...
Got that right...and if they don't receive the right nurturing to counteract it, they grow up to be liberal Socialists...