A great analogy for PTC thermistors would be an open water faucet that allows the water to flow. The open faucet is like the PTC in its low resistance state. The flowing water is like the electricity moving through the ceramic. However, when the circuit is energized with sufficient power, the PTC heats up almost instantaneously increases the resistance. The high resistance essentially causes the electricity to cease “flowing” through the part. This would be analogous to shutting the water faucet off so that the flow of water stops.