(d) The _probability of success_ or the opposite in any line of personal services, is a circumstance that has some influence on the rate of wages paid in it, through the action of this probability on the numbers of those who enter upon it. If ultimate success be doubtful, fewer persons will naturally engage in such a business, and those who dare in it and succeed, will probably reap a very high reward. So, also, those who take jobs by the contract, and therein assume more or less of risk, are commonly paid at a higher rate for their services than those who do similar work by the day. It is true, that this is owing partly to the fact that the contractor usually puts in his own capital more or less, and must therefore be paid profits as well as wages, and also that the wages of superintendence are due to him in addition to ordinary wages; still, there is a residuum of difference, which can only be accounted for by the risk he runs of a successful issue of his contract. The general variation in Supply and wages from this fourth cause, would certainly be greater than it is, were it not for the overweening confidence which men in all generations seem to have in their own good luck. This excess of worldly faith is always seen in the rush which is made for newly discovered mining regions. It was seen to perfection in 1889 in the uncontrollable advance of thousands _into_, and their almost immediate exit _out of_, the then just opened territory of Oklahoma. The facility with which lottery tickets are sold even yet in many countries proves the prevalence of this over-confidence. It is demonstrable beforehand on the doctrine of Chances, that no person can rationally buy _any_ lottery ticket at its advertised price, because if that person should buy all the tickets advertised he would certainly lose money, since the sum of the prizes is always less than the sum of the prices. Otherwise the projectors of the lottery would always lose money.