Let us first take the case where the choice discrepancy becomes ever smaller as the generations go by. It will eventually become so small that the pull of female preference in one direction is exactly balanced by the pull of utilitarian selection in the other. Evolutionary change will then come to a halt, and the system is said to be in a state of equilibrium. The interesting thing Lande proved about this is that, at least under some conditions, there is not just one point of equilibrium, but many (theoretically an infinite number arranged in a straight line on a graph, but there's mathematics for you!). There is not just one balance point but many: for any strength of utilitarian selection pulling in one direction, the strength of female preference evolves in such a way as to reach a point where it balances it exactly.
So, if conditions are such that the choice discrepancy tends to become smaller as the generations go by, the population will come to rest at the 'nearest' point of equilibrium. Here utilitarian selection pulling in one direction will be exactly counteracted by female selection pulling in the other, and the tails of the males will stay the same length, regardless of how long that is. The reader may recognize that we have here a negative-feedback system, but it is a slightly weird kind of negative-feedback system. You can always tell a negative-feedback system by what happens if you 'perturb' it away from its ideal, 'set point'. If you perturb a room's temperature by opening the window, for instance, the thermostat responds by turning on the heater to compensate.
