James, women often complain that their husband skimps on foreplay. The reason is that he finds foreplay so boring that he will lose his erection unless he hurries on to the main event. Our sex instincts were formed during all those millennia when life was too short for long-standing unions. Also, because so many women perished in childbirth, men might have several fresh mates--and all that excitement and discovery--in a lifetime. I wish Eros lasted longer, but we can't change how we are wired. Nor can we command the appearance and disappearance of erections. When they are unreliable, we are just as frustrated and humiliated as our women.