We humans rely on networks of communication to survive. From your friend in the next village you might hear about the new lions or the war coming your way. Once you see it with your own eyes it will be too late. Hearing about new diseases before they come have saved countless lives. A single human is weak, but as a community we will head to the stars.
Sometimes we are warned about imaginary dangers too. Look at the "ghost rape" and "penis theft" hysterias that sweep through some cultures regularly. Yes, some dangers are already upon you by the time you see them, but other times a society is almost destroyed because of a "danger" that doesn't exist. Panic is almost never a smart behavior.