What a weird false dichotomy. A planet with well over 7 Billion people can do at least two things at once.
You are correct in general, but one cannot do two things at once when the first thing is (at least, arguably) a necessary prerequisite to the second thing.
It is worth noting that the more fundamental thing going on here is that abstract syntax trees are the general way in which programs are represented after being parsed, rather than this being something specific to Lisp. What makes Lisp interesting is essentially that it uses a notation that makes the underlying AST incredibly explicit.
As someone who regularly has to deal with code that has been broken needlessly into smaller functions so that I have to constantly jump around to figure out what is going on, this really resonates with me.
The latest case was someone who took something that really only needed to be a single function and instead turned it into a class with a dozen tiny methods.
I stand corrected.
Happy cake day!