> If you don't understand why cons is important, and the appropriate places to use it, then you really don't understand Lisp.

Lisp-the-mathematical-model, perhaps, but not Lisp-the-programming-language.

Conses are definitely a fundamental idea, and they're obviously how source code is written, and it's nice that they're around — but honestly for real work it's unlikely that most data will live in cons structures (unless of course the higher-level data structures actually are built from conses, which of course they could be).