A man is fit for neither business nor pleasure, who either cannot, or does not, command and direct his attenti0on to the present object, and, in some degree, banish for that time all other objects from his thoughts. If at a ball, a supper, or a party of pleasure, a man were to be solving, in his own mind, a problem in Euclid, he would be a very bad companion, and make a very poor figure in that company; or if, in studying a problem in his closet, he were to think of a minuet, I am apt to believe that he would make a very poor mathematician. There is time enough for everything in the course of the day, if you do but one thing at once; but there is not time enough in the year, if you will do two things at a time.

Lord Chesterfield (1694-1773) English statesman, wit [Philip Dormer Stanhope]

Letter to his son, #121 (14 Apr 1747)
    (Source)