Item. One of the most effective forms of industrial or military sabotage limits itself to damage that can never be thoroughly proven - or even proven at all - to be anything deliberate. It is like an invisible political movement; perhaps it isn't there at all. If a bomb is wired to a car's ignition, then obviously there is an enemy; if a public building or a political headquarters is blown up, then there is a political enemy. But if an accident, or a series of accidents, occurs, if equipment merely fails to function, if it appears faulty, especially in a slow fashion, over a period of natural time, with numerous small failures and misfirings - then the victim, whether a person or a party or a country, can never marshal itself to defend.

In fact, Arctor speculated as he drove along the freeway very slowly, the person begins to assume he's paranoid and has no enemy; he doubts himself. His car broke down normally; his luck has just become bad. And his friends agree. It's in his head. And this wipes him out more thoroughly than anything that can be traced. However, it takes longer. The person or persons doing him in must tinker and putter and make use of chance over a long interval. Meanwhile, if the victim can figure out who they are, he has a better chance of getting them - certainly better than if, say, they shoot him with a scope-sight rifle. That is his advantage.

[Philip K. Dick, A Scanner Darkly, Vintage Books 1991, 91f]