How do TVS diodes (ESD protection diodes) work?

Let’s consider how electric current flows in a circuit when an electronic device is operating normally (blue line) and when it is exposed to static electricity (red line).
While an electronic device is operating normally, TVS diodes remain off and exhibit parasitic (junction) capacitance, thereby acting as capacitors.
When voltage greater than a certain voltage is applied to TVS diodes, current suddenly begins to flow through the TVS diodes. Therefore, when the voltage by ESD enters the circuit, current flows through the TVS diodes, causing voltage to remain constant, thus protecting the following ICs and other components from excessive voltage and current.