 Behavior in the face of risks tends to follow what is known in psychology as prospect theory; People tend to be more averse to harms which are certain than more severe harms which are merely probable.According to Prospect Theory, coerced abstinence is effective at getting people off drugs because the frequency and certainty of a sentence is a much more significant deterrent than severity of the sentence.In other words, if virtually every time probationers fail a drug test, they go immediately to jail (even for just a few days) probationers will use less drugs than if they are only occasionally caught even if the penalty is significantly higher.