The Law of Detachment

The 6th spiritual Law of Success, Law of detachment seems to be a tough concept for me to grasp.  Does Law of Detachment mean you submit your desire to the universe and just trust it to manifest.  Or does it mean that what your desire should not define who you are.  For example, if you want a car, you should not think that without this car your happiness will not be fulfilled.  Instead you  should believe without any doubt in your heart and soul that the universe will manifest this car for you in some way.