There probably isn't a single example. But "quantity is a quality in itself". Classes sort of evolve when you need to manage dozens or hundreds of those associative arrays and don't want to keep in your head exactly what keys are in a given array. And when you have a dozen of arrays and a hundred of functions, which functions go with each array.
In itself every element is easy, but together they are hard.
In itself every element is easy, but together they are hard.