Why would one headlight not work on low beam but both work on high beam?

If one headlight works on high beam but not on low beam, it typically indicates a problem with the low beam socket, the bulb, or the wiring specific to the low beam circuit. The high beam setting often bypasses certain components, allowing both headlights to function even if one low beam is faulty. It could also be due to a blown fuse or a bad connection in the low beam circuit. Checking the bulb and connections for the non-working low beam is a good first step in troubleshooting.