Carrots give you excellent night vision

What actually happened

There is a real nucleus. Vitamin A is a component of rhodopsin, the pigment your rod cells use in dim light, and severe deficiency causes night blindness, a serious problem in parts of the world where it remains a leading cause of preventable childhood blindness. Correcting a deficiency genuinely restores vision.

What does not follow is that surplus helps. Once your stores are adequate, more beta-carotene gives you nothing except, at high enough doses, orange-tinted skin. The superhero version of the claim was amplified during the Second World War, when the British Ministry of Information promoted stories about carrot-eating pilots with exceptional night vision, which had the useful side effect of not drawing attention to the newly developed airborne radar that was actually responsible. Historians debate how much the Germans were fooled. The British public was thoroughly convinced, and so was your school.