Stepped Leader
Lightning does not throw its light down. A leader descends in small tentative steps, feeling for the strongest way, branching where the choice is close. Only when a path is complete does the return stroke travel it, all at once, upward. The flash everyone sees is the last thing that happens.
Hold high to charge, release to strike · tap low to plant the rod
The physics here is the dielectric breakdown model of Niemeyer, Pietronero and Wiesmann, from 1984: relax an electric potential around a growing conductor, then let the conductor grow one site at a time, choosing among its neighbors with probability weighted by the local field raised to a power. That single exponent decides everything. Near one, the discharge grows as dense moss; higher, it thins into the sparse nervous darts of a real strike.
A real stepped leader descends from the cloud in segments of some fifty meters, pausing between steps, almost too faint to see. When it connects, the return stroke drains the whole channel from the ground up at a third the speed of light, and that is the light called lightning. The rod is real physics too: a grounded point concentrates the field above it, which is why the path so often ends there. What stays on this canvas after each strike is the part nature keeps too, in glass and skin and wood: the Lichtenberg figure, the signature of the path that was found.