is that energy and industry which we show when we do what we like (Latin, diligo, I like); but indolence is that listless manner with which we do what thoroughly vexes us. (Latin, in, intensive; dolco, to grieve.)
A four-wheeled stage-coach, drawn by four or more horses. Common in France before the introduction of railroads. The pun is well known.
Si vis placere magistro, utere diligentia (i.e. his diligence).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894