What one loses on the swings one makes up on the roundabouts

The proprietor of a fair ground does not mind running his swings at a loss if his roundabouts bring him in a handsome profit. He can afford to provide swings for the few people who enjoy them and who will very likely pay to go on the roundabouts as well. Similarly a newsagent may make a much smaller profit on newspapers good for trade because customers who call in for them will often buy other things at the same time. Another aspect of the proverb is that although the swings make less profit than the roundabouts today, they may make more profit than roundabouts tomorrow.