It could be assumed that a certain ignition voltage is provided, which is far above the required and thus ensuring that a stable ignition is always garanteed. In reality, however, it is the other way around. Perhaps you can compare it with a trip through the jungle, where you have to clear the way with the machete.

There is for the electrons a certain distance through the air from one electrode of the spark plug to the other. Before they can overcome these, a kind of channel must be created, which ensures an electrical connection. During the build-up, the number of jump-ready electrons is getting larger and increasing the voltage.

The flashover is favored by sharp edges or even peaks on the electrodes (picture above), a reason why older spark plugs have a significantly higher ignition voltage requirement than new ones. The choice of materials for the electrodes can also play a role here. Also, of course, mixture prepartion, combustion room pressure, and electrode spacing. The level of the ignition voltage thus depends on the need to "ionize" the spark gap.

Measuring directly on the spark plug, a very high ignition voltage can be expected after ionization, which then falls back to values of up to a maximum of 1 kV. The current flow with sparking is ensured. It can take place from the center to the ground electrode(s) or vice versa. It is said that an old spark plug can require 25 percent or more ignition voltage. 09/17