There is a difference between a breaker that trips because a circuit is genuinely overloaded and one that trips because a protective device is reacting to something it was designed to react to. The second kind is frustrating precisely because nothing appears to be wrong.
Ground-fault protection watches for an imbalance between current going out on the hot and returning on the neutral, and it opens at around five thousandths of an amp. Motors with older windings, heating elements with slightly damp insulation, and long outdoor cable runs all leak small amounts of current to ground as a normal part of ageing. Individually each leak is below the threshold. Several on the same circuit can add up past it.
Arc-fault protection listens for the electrical signature of arcing, and it has to distinguish a dangerous arc in a damaged cable from the harmless arcing produced by a brushed motor, a switch contact or a dimmer. Vacuum cleaners, some power tools and certain older appliances produce signatures close enough to cause a trip.
Shared-neutral circuits are a specific case. Where two circuits share one neutral conductor, protective devices see current that does not balance against their own hot conductor, and the result is immediate tripping unless a two-pole device designed for that arrangement is used.
Diagnosis follows a pattern. Unplug everything on the circuit and reset. If it holds, add loads back one at a time until it trips, which usually identifies a single appliance. If it trips with nothing connected, the fault is in the wiring rather than the equipment.
What matters is resisting the temptation to substitute a standard breaker to make the problem stop. The device is reporting something. Sometimes what it is reporting is a marginal appliance, and sometimes it is a damaged cable inside a wall, and the two look identical from the panel.
Age is worth factoring in as well. Protective devices have a service life of their own, and one that has been in place for fifteen years in a damp location can start tripping without any external cause. Testing with the button monthly is the recommendation on the label, and a device that fails to reset after a test has told you something useful.
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