That’s a good question—it’s annoying to have to reset a circuit breaker because of a power overload.
First, it’s important to note that each breaker on your distribution panel is designed to prevent electric wires from overheating. When the amperage exceeds the breaker’s capacity, it automatically trips and cuts off electric current to keep the wires from overheating.
To get back to your question, the maximum load a 15-amp breaker can handle, at a tension of 120 volts, is officially 1800 watts. However, it is strongly recommended that you limit the maximum load on a single circuit to 1,500 watts.
Most home devices (coffee machine, toaster, space heater, hairdryer, microwave oven) have a maximum power consumption of 1,500 watts. You therefore shouldn’t use them at the same time on the same circuit.