To look out for one’s own best interest or for the opportunity that will be most profitable. The term is thought to come either from betting in cockfights (main being an obsolete word for cockfight) or from a game of chance called hazard, in which the main signified the number (anywhere from 5 to 9) called by the caster before the dice were thrown and chance signified the second throw of the dice, which determined the total. In any event, the expression dates from the sixteenth century, was recorded by John Lyly and Shakespeare, among others, and appeared in John Ray’s English Proverbs of 1670.