It's very important to understand that '... which means (quote ...) is not a shorthand for making lists. It's a form which causes lisp to return, unevaluated, the object that was created by the lisp reader. If you quote a list and then modify the quoted list, it stays modified. If you want to create a list and then modify it, create it with (list ...).
Be sure to go over the distinct read and eval phases of lisp
execution. Once you understand the distinction, quote will make
much more sense.
(defun foo () (list 'a 'b 'c)) => foo
(defun bar () '(a b c)) => bar
(foo) => (a b c)
(bar) => (a b c)
(delq 'b (foo)) => (a c)
(delq 'b (bar)) => (a c)
(foo) => (a b c)
(bar) => (a c)
(symbol-function 'foo) => (closure (t) nil (list 'a 'b 'c))
(symbol-function 'bar) => (closure (t) nil '(a c))