One of the most common service calls electricians get is about what appears to be a failure in a bathroom circuit. By code, all outlets within 6 feet of a water source are required to be protected by a ground fault circuit interrupt (GFCI).
These are important safety devices that cut off power if a circuit is losing amperage, so GFCIs are most commonly seen in bathrooms and exterior outlets. The thing that your electrician wants you to remember is that a single GFCI device protects everything else “downstream” on that circuit.
Because bathrooms are often not on an isolated circuit, that means a triggered GFCI will kill the power to outlets and lights that may seem unrelated. And things can be even more confusing when the GFCI is installed at the electrical breaker box itself.