The degree of responsibility attributed to the successful and unsuccessful assassins may depend not so much on the fact that they both tried to kill as on the fact that they were both willing to kill.
But now consider a different would-be assassin who does not even try to kill anyone, but only because his circumstances did not favor this option. This would-be assassin is willing to kill under favorable circumstances (and so he may seem to have had good circumstantial moral luck since he was not in those circumstances). Perhaps the degree of responsibility attributed to the successful and unsuccessful assassins described above depends not so much on the fact that they both tried to kill as on the fact that they were both willing to kill; in this case, the would-be assassin just introduced ma...