It's not actually rational, let alone long-term optimal, to act as though there is a predator behind every bush given a 1% (in reality it's probably a couple of orders of magnitude less likely, but we'll ignore that). If you need water and head for the local watering hole, avoiding bushes will most likely result in you not getting water since bushes tend to grow where there is water. I may be 1% likely to get eaten by something hiding behind the bush but I am 100% likely to die if I don't drink water.

Avoidance of all possible risk is a recipe for paralysis. Part of being rational is evaluation of risks vs rewards as well as recognizing the dangers of unintended consequences and the fact that nearly all meaningful decisions are made with incomplete information and time limits.