The problem is not in marriage, but in sex; and would be felt under the freest concubinage. Nevertheless, the overwhelming mass of mankind has not believed in freedom in this matter, but rather in a more or less lasting tie. Tribes and civilizations differ about the occasions on which we may loosen the bond, but they all agree that there is a bond to be loosened, not a mere universal detachment. For the purposes of this book I am not concerned to discuss that mystical view of marriage in which I myself believe: the great European tradition which has made marriage a sacrament. It is enough to say here that heathen and Christian alike have regarded marriage as a tie; a thing not normally to be sundered. Briefly, this human belief in a sexual bond rests on a principle of which the modern mind has made a very inadequate study. It is, perhaps, most nearly paralleled by the principle of the second wind in walking. The principle is this: that in everything worth having, even in every pleasure, there is a point of pain or tedium that must be survived, so that the pleasure may revive and endure. The joy of battle comes after the first fear of death; the joy of reading Virgil comes after the bore of learning him; the glow of the sea-bather comes after the icy shock of the sea bath; and the success of the marriage comes after the failure of the honeymoon. All human vows, laws, and contracts are so many ways of surviving with success this breaking point, this instant of potential surrender.