Once the battle is joined and a tactic is employed, it is important that the conflict not be carried on over too long a time. …There are many reasons of human experience arguing for this point. I cannot repeat too often that a conflict that drags on too long becomes a drag. The same universality applies for a tactic or for any other specific action.
Among the reasons is the simple fact that human beings can sustain an interest in a particular subject only over a limited period of time. The concentration, the emotional fervor, even the physical energy, a particular experience that is exciting, challenging, and inviting, can last just so long — this is true of the gamut of human behavior, from sex to conflict. After a period of time it becomes monotonous, repetitive, an emotional treadmill, and worse than anything else a bore. From the moment the tactician engages in conflict, his enemy is time.
BTW Alinsky (b.1909) wrote this book to try to stop baby boomers from being dumb and fouling everything up. I am not a huge fan of the intergenerational model of class conflict but I think it is interesting.