Lisp Coerce and Set function explanation

Question

I try to do this directly to the interpret:

(setf example (coerce "blablabla" 'list))

and works fine. Infact (car example) returns #\b

but if I try this:

(defun myfun (string) ( (setf example (coerce string 'list))))

(myfun "blablabla") 

I don't get the same!

How can I fix?