I think like many programmers are "bottom up" (including me), I had a hard time understand virtual methods until I read an example on how they were implemented,

I think like many programmers are "bottom up" (including me), I had a hard time understand virtual methods until I read an example on how they were implemented, then I was able to understand what it was and then the explanation why they were useful. I remember two lessons about networks at school, the first one was "top to bottom" (layer 7 to layer 1), I understood nothing, then there was another one bottom up, and I finally understood networks..