While flying, you might have been asked by a flight attendant to open the window blinds. In fact, those blinds have to be open during a take-off and landing. But why does this need to be done?
The first reason is your safety. If anything happens during a take-off or landing, your eyes will already be used to the day or night light outside, thus you will be able to react more quickly.
Another reason for keeping the blinds open is visibility of aircraft outside. If any problems occur with the engine or wings, the crew can see it out of those tiny round windows in a cabin. If the aircraft needs to be evacuated, passengers and the whole crew is able to see which side of the aircraft is safer for evacuation.