Answer:
The trade-off hypothesis argues that pathogens tend to evolve toward ever decreasing virulence because the death of the host (or even serious disability) is ultimately harmful to the pathogen living inside. For example, if the host dies, the pathogen population inside may die out entirely. However, some pathogens evolve greater levels of virulence under the trade-off hypothesis. This is an example of short-sighted evolution.
Short-sighted evolution is a type of selection that favors traits that are beneficial in the short term but harmful in the long term. In this case, pathogens that evolve greater levels of virulence are able to reproduce more quickly and produce more offspring before the host dies. However, this strategy is not sustainable in the long term because it leads to the death of the host and ultimately the pathogen itself.