An ordered pair is a useful data structure, and it's beneficial to have special short names for accessors to its elements. Humanity got very lucky with the names “car” and “cdr”. Naggum does point that out.

Any rule about any language could be labeled a barrier to its success because any such rule contributes to the cognitive load, making learning the language slightly more difficult than it would be without that rule. What matters more is how much cognitive load is there after you learn the rules. Common Lisp is very successful at it.