Mirrors show things where they can't be. Mirages decieve us about the distant landscape. Fish in ponds appear higher in the water than they are. The moon just above the horizon appears much larger than it should. The rising or setting sun looks redder than it really is.
Parallel lines appear to converge to the horizon.
Rainbows aren't tangible. Lenses alter the apparent size and distance of objects. Most of these are physical illusions , caused by physical effects on the light as it travels from an object to our eyes, and we are not fooled by them. We know that distant objects are much larger than they appear to be. We know that objects seen in mirrors are actually in front of the glass, not behind it.