Mencius - Book 1, Part 1, Chapter 7E

The king asked, 'How may the difference between the not doing a thing, and the not being able to do it, be represented?

Mencius replied,'In such a thing as taking the T'âi mountain under your arm, and leaping over the north sea with it, if you say to people -- "I am not able to do it," that is a real case of not being able. In such a matter as breaking off a branch from a tree at the order of a superior, if you say to people -- "I am not able to do it," that is a case of not doing it, it is not a case of not being able to do it. Therefore your Majesty's not exercising the royal sway, is not such a case as that of taking the T'âi mountain under your arm, and leaping over the north sea with it. Your Majesty's not exercising the royal sway is a case like that of breaking off a branch from a tree.

'Treat with the reverence due to age the elders in your own family, so that the elders in the families of others shall be similarly treated; treat with the kindness due to youth the young in your own family, so that the young in the families of others shall be similarly treated: do this, and the kingdom may be made to go round in your palm.
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.