Some systems have multiple states, even under identical conditions. If you plot a curve of their behavior, it's not a simple single-valued function — it bends back on itself.
Consider a gasoline engine in an automobile. At a given speed, there are usually two possibilities: the engine can be running efficiently, or you can be "on the wrong side of the power curve", in a state where a lot of gas is being wasted and not much energy is coming out. Pressing harder on the accelerator in the second case won't do any good — it just makes things worse.
In the same way, a piece of iron has something like a memory of the magnetic fields it has been through, so the current state shows evidence of the past. A tax system can yield different revenues with the same rates, depending on taxpayers' choices of activities. An airplane can be flying level either mushing along at a dangerously high angle of attack, or going fast with low drag and the nose down.
Hysteresis is the technical term for this sort of history-dependent behavior. People show hysteresis too: how they get to a place influences how they act. Treat them fairly, and they'll tend to reciprocate. But we can't expect them to instantly forget historical wrongs, even if their current circumstances are identical to those of others who haven't been through such a past. Should everybody "forgive and forget"? Perhaps — but perhaps such magnanimity isn't something we can legitimately ask of anyone else. Forgiveness is a gift, not an obligation.
Friday, June 18, 1999 at 19:22:50 (EDT) = 1999-06-18
(correlates: StaticActors, 2004-11-03 - Leaf Blower Day, MagneticStuds, ...)