(d) _There were also two reciprocal estimates_, the estimate of King Hiram of all the efforts requisite to cut and hew and float the timber, as compared with the aggregate of efforts needed to obtain the necessary wheat and barley and wine and oil in any other possible way; and the estimate of King Solomon of all the labors required to grow and market these agricultural products, as compared with what would otherwise be involved in getting the much-wished-for timbers. Such estimates invariably precede every rational exchange of products. It is not in human nature to render a greater effort or the result of it, when a lesser effort or the result of it will as well procure the satisfaction of a desire. Efforts are naturally irksome. No more of them will ever be put forth than is necessary to meet the want that calls them forth. No man in his senses will ever put more labor on anything, with which to buy something else, than is necessary to get that something else by direct effort or through some other exchange. Here we are on ground as solid as the very substance of truth can make it. The Jews of Solomon's time were too shrewd and sparing of irksome labor to devote themselves for years to the toils of the field and of the vat to get by traffic the materials for their temple, if they could have gotten those materials by a less expenditure of toil in any other way. Those Phoenicians of Tyre and Sidon, the born merchants of the East, the founders of commercial Carthage in the West, if they could have extorted from the reluctant sands of their coast the cereals and the vines and olives requisite for their own support with only so much of exertion as was needed to get that to market with which to buy them, would never have taken the indirect in preference to the direct method. They took the indirect, because it was the easier, and therefore the better. It may, accordingly, be laid down as a maxim, that men never buy and sell to satisfy their wants but when that is the easiest and best way to satisfy them. It saves effort. It saves time. It saves trouble. It divides labor. It induces skill. It propels progress. But in order to determine which may be the easier way, requires constant _estimates_ on the part of each party to a possible trade. Shall I shave myself or go to the barber? Before I decide, I estimate the direct effort in the light of the effort to get that with which to pay the barber for his service. If I trade with him, it is because I deem it easier, cheaper in effort, more convenient in time. Trade means comparisons in every case--comparisons by both parties--and in the more recondite and complicated cases, elaborate comparisons and often comprehensive calculations involving future time.