As written by CronoDAS. If most people get a debilitating disease by age X it would be widely accepted as unavoidable. Used to be the case with losing teeth in old age, still is with dementia and aging. Basically a comparison of the own experience to the common experience of your peers.
As everyone here knows, it would be a stupid idea to switch from airplanes to cars out of safety/terrorism concerns: Cars are a much more risky means of transportation than airplanes. But what other major risks are there that many people systematically undervalue or are not even consciously aware of?
The same can be asked for chances.