What happens if you put a 100 watt bulb in a 60 watt socket?

Putting a 100-watt bulb in a 60-watt fixture could cause intense heat, melting the light socket and the insulation on the fixture's wires. Any time you have that kind of damage on wires, you're at a big risk for arc faults, where an electrical current falls off its intended path— a leading cause of home fires.