A non-virtual function says, you have to do this and you must do it this way. A virtual function says you have to do this, but you don't have to do it this way. That's their fundamental difference.

Lightstone's Convolution Principle: The concurrent development of multiple features operating on intersecting componentry will take longer to complete than the sum of the schedule estimations for each.

Friends, much as in real life, are often more trouble than their worth.

... the results are undefined, and we all know what 'undefined' means: it means it works during development, it works during testing, and it blows up in your most important customers' faces.

Do that, and the best you can hope for is that people will ignore you. More realistically, you'd be skinned alive, or possibly sentenced to ten year hard labor writing microcode for waffle irons and toaster ovens.

A non-virtual function says, you have to do this and you must do it this way. A virtual function says you have to do this, but you don't have to do it this way. That's their fundamental difference.