This defect is avoided in a modification of the theory that a recent writer has adopted. “The antithesis,” says Mr. Stout,[137] “between pleasure and pain is coincident with the antithesis between free and impeded progress towards an end. Unimpeded progress is pleasant in proportion to the intensity and complexity of mental excitement. An activity which is ... thwarted and retarded ... is painful in proportion to its intensity and complexity and to the degree of the hindrance.” Mr. Stout admits the difficulty of applying this principle of explanation to the pleasures and pains of sense:[138] and--unlike Hamilton--he expressly recognises that “a struggle with difficulties which is not too prolonged or too intense may enhance the pleasure of success out of all proportion to its own painfulness.” But this qualification seems to render the propositions first laid down unimportant from our present practical point of view, whatever may be their theoretical value. I think, too, that the importance of antecedent desire, as a condition of the pleasures and pains attendant on voluntary activities, should be more expressly recognised. When desire is strong, hopeful effort to overcome difficulties in the way of fruition tends to be proportionally pleasurable--apart from actual success--while disappointment or the fear of disappointment similarly tends to be painful: but when desire is not strong, the shock of thwarted activity and unfulfilled expectation may be rather agreeable than otherwise. Thus, suppose I take a walk for pleasure, intending to reach a neighbouring village, and find an unexpected flood crossing my road; if I have no strong motive for arriving at the village, the surprise and consequent change in the plan of my walk will probably be on the whole a pleasurable incident. The importance of eager desire as a condition of pleasure is noteworthy from an ethical point of view: as it gives the psychological basis for the familiar precept to repress--with a view to private happiness--desires for ends that are either unattainable or incompatible with the course of life which prudence marks out; and for the somewhat less trite maxim of encouraging and developing desires that prompt in the same direction as rational choice.