Undeniable universal truth. I sometimes find myself making plans based on the fact that the most annoying possible outcome is also the most likely one.
The car gets dirty again when it rains and when it gets dry again. I guess dust, salt, pollution and more is what gets mixed in and put on the chassi as it rains, falls from roofs and splashes, but can't say I've investigated deeply enough. Not the end of the world, just annoying it keeps happening.