According to this rule, men should be rewarded in proportion to their contributions to the product. It is open to the obvious objection that it ignores the moral claims of needs and efforts. The needs and use-capacities of men do, indeed, bear some relation to their productive capacities, and the man who can produce more usually needs more; but the differences between the two elements are so great that distribution based solely upon productivity would fall far short of satisfying the demands of needs. Yet we have seen that needs constitute one of the fundamentally valid principles of distribution. Between productivity on the one hand and efforts and sacrifices on the other, there are likewise important differences. When men of equal productive power are performing the same kind of labour, superior amounts of product do represent superior amounts of effort; when the tasks differ in irksomeness or disagreeableness, the larger product may be brought into being with a smaller expenditure of painful exertion. If men are unequal in productive power their products are obviously not in proportion to their efforts. Consider two men whose natural physical abilities are so unequal that they can handle with equal effort shovels differing in capacity by fifty per cent. Instances of this kind are innumerable in industry. If these two men are rewarded according to productivity, one will get fifty per cent. more compensation than the other. Yet the surplus received by the more fortunate man does not represent any action or quality for which he is personally responsible. It corresponds to no larger output of personal effort, no superior exercise of will, no greater personal desert. It is based solely upon a richer physical endowment by the Creator.