Although an ounce of prevention may often be worth a pound of cure, there is an inherent and unfortunate tendency for prevention to be discouraging. Only in the midst of an epidemic are preventive efforts likely to be visible and dramatic. In most situations, something that is prevented is a nonevent. Individuals can hardly be expected to be aware of nonevents: these can be detected only by statistics. As a consequence, the benefits of prevention are more likely to appeal to our intellect than to our emotions.
Bad effects, on the other hand, are usually readily recognized. Because they are likely to occur in close temporal association with the preventive procedure, they are perceived as resulting from that procedure even when they are merely coincidental. Their emotional effects can be severe, the more so because something bad happened when good was expected.
Prevention of tuberculosis by giving isoniazid to persons
Comstock GW. Prevention of Tuberculosis Among Tuberculin Reactors: Maximizing Benefits, Minimizing Risks. JAMA. 1986;256(19):2729–2730. doi:10.1001/jama.1986.03380190099036