The Metaphysical Elements of Ethics by Immanuel Kant Chapter 4 Page 2

and to regard myself as in duty bound to promote it. For it is just in this that the perfection of another man as a person consists, namely, that he is able of himself to set before him his own end according to his own notions of duty; and it is a contradiction to require (to make it a duty for me) that I should do something which no other but himself can do.