A couple in tune with each other - conciliatory objects

A cigarette for two is always a good sign... Or not.

One of the basis for a good relashionship, as a couple, is the ability that both parties should have to share... Or is it? You could say, in all fairness, that sharing certain objects, given the selfishness innate to every human being, will, sooner or later, spike up a fight. The insane proposal of this inventor is that for some things to be shared, they should be different. They should have a characteristic that would allow their simultaneous use! Why not?