1.1.1.15. A thing’s intrinsic final end is to do its own act well.

"The purpose of the knife is not just to cut, but to cut well. To do its own act well, a thing needs a certain quality or qualities, traditionally called ‘virtues.’ The virtue of a knife is sharpness because sharpness is the quality that enables a knife to cut well. So we can say that the intrinsic good of anything that has an act of its own is to do its own act with its own virtue."