I'm almost sure that my copy of the GoF book did have that sentence as the only one on its page, and as I said earlier, it was on a separate page before the mai

I'm almost sure that my copy of the GoF book did have that sentence as the only one on its page, and as I said earlier, it was on a separate page before the main body of text, i.e. even before chapter one. Maybe we have different editions. Could still be wrong about that, though. E.g. it could been a different book, not GoF, although I think it unlikely. Why I say that I remember it being so, is because I once mentioned this to a startup founder I was consulting to, maybe because he had written some code that used inheritance unnecessarily, and I said it to him in that context, during a design discussion, and suggested we follow the guideline (to prefer composition over inheritance). He was impressed (I mean by the guideline, not me) and we did follow it from then on.