Why flies can never find the open window?
Flies have compound eyes that allow them to distinguish light and dark very accurately. When roaming around your room, the only thing they are looking for is a source of light. Even though an open window is a source of light, it also provides a flow of air from outside into the room. This wind creates an atmosphere that the insect is not very keen to fly in, which causes it to avoid your window and look for another source of light.