variable's documentation string

[TheFlyingDutchman]

If I declare a variable:
(defvar myVar 2 "This is the documentation string)

According to the way I read the GNU Emacs Lisp Reference manual I
should be able to retrieve this string with:

(message "the docstring for %s is %s" 'myVar (documentation-property
'myVar 'variable-documentation))

but the output is

the docstring for myVar is nil


Does anyone know what I am missing or doing wrong?