What is the brightest sign of a pirate? An eye patch, of course, if you don't take the huge amount of rum they drank. The phenomenon of the bandage is not unique, it is invariable and has already become a kind of custom. Why do pirates wear a bandage? The simplest answer that instantly comes to mind is, "They don't have an eye?" Not true.
So, the real version of wearing an eye patch tells us why pirates and some sailors still wore it. This was done for convenience - it is always very gloomy and dark in the ship's holds, and when people descended from the deck, their eyes had to adapt for a long time. And if one eye is blindfolded and did not see the light on the deck, then in the dark in a matter of seconds you can perfectly orient yourself. This was very useful in various extreme situations when it was necessary to make an important decision clearly and quickly.
These armbands began to be used with the development of airplanes. When the pilots flew over bright cities with many glowing lights, they looked at space with one eye, and with the other (from under the bandage) at instruments or maps in a cockpit devoid of light.