But that the course of true love does generally not run smooth is understood, more or less, by every one. And it is woman’s strange and imperious instinct—even though at considerable suffering to herself—to see that it _doesn’t_ run smooth. Ellis practically bases[24] the whole of the evolution of modesty on this instinct—reaching far down in the animal kingdom—by which the female constantly throws difficulties and obstacles in the way of courtship (by her coynesses, contrarieties, changeable moods, and so forth); thus calling out in the male all his ingenuity, his impetuosity, his energy, in overcoming them; rousing dormant elements of his nature; delaying consummation and giving time for his character and all his qualities to concentrate; and indirectly having a like effect upon herself. So that ultimately by this method a maximum of passion and agitation is produced, and in the case of the human being love penetrates to the very deeps and hidden caverns of the soul. Such is the genesis of Modesty—not by any means Nature’s _denial_ of love, but rather the crafty old dame’s method of rendering love, by temporary obstacles, all the more insurgent and irresistible—her method of making it less superficial, of deepening the channels and rendering them more profound. Practically, and as a matter of policy, a too easy consent to another’s love is a mistake. The barb only sticks when the bait is withdrawn. Ovid, it will be remembered, advises that “the lover should be admitted by the _window_, even when the door is quite accessible, and really more convenient”;[25] and most girls (though they have not read Ovid) know instinctively that this is the right policy! Nothing is so hateful to a real lover as an easy, accommodating, altruistic affection—thoroughly Christian in sentiment, and with no more shape of its own than a pillow! Romance flies at the mere mention of Christian altruism; and the essence of love is romance. Hence not only technical obstacles, but essential differences are necessary to the growth of the passion. Differences of age, differences of sex, differences of class, temperament, hereditary strain, learning, accomplishment, and so forth—if not _too_ great—are all necessary and valuable. They all mean romance, and contribute to that exchange of essences which we saw was the primitive protozoic law. It is quite probable that the abiding romance between the sexes—so much greater as a rule than that between two of like sex—is due to the fact that the man and the woman never really understand each other; each to the other is a figure in cloudland, sometimes truly divine, sometimes alas! quite the reverse; but never clear and obvious in outline, as a simple mortal may be expected to be.