Somewhat relatedly, a very common mistake in Lisp is modifying literals; a lot of people don't realise that there's a difference between writing '(a b c) and writing (list 'a 'b 'c), but QUOTE's description in the spec plainly says "The consequences are undefined if literal objects (including quoted objects) are destructively modified." To demonstrate the difference in practice (DELETE is the destructive version of REMOVE):

    CL-USER> (defun abc-without (letter) (delete letter '(a b c)))
    ABC-WITHOUT
    CL-USER> (abc-without 'a)
    (B C)
    CL-USER> (abc-without 'b)
    (A C)
    CL-USER> (abc-without 'c)
    (A)

This behaves strangely because it modifies the constant list (A B C) rather than consing up a new one on each invocation (like calling LIST or COPY-SEQ would), so by the end the list it passes to DELETE has been reduced to (A).