Only The Strong Survive
Natural Selection in evolution dictates that only the strong will survive. This is not meant to be that a powerful species will survive, though this can be useful. Rather, we use “strong” in this area merely means a species will be capable of getting through problematic issues it might face.
Therefore, it “evolves” to be capable of this. Whether that evolution is present in a small, medium, or large way, it is crucial to survival just the same. In fact, a small change over a long period of time will turn into a large evolutionary change eventually. This is where the real sad part comes into play. Sticking with the eyesight example, if one needs to have better eyesight but cannot develop this, it will die.