Documentation is all you need - or how I stopped suffering with legacy code

Author here. In corporate engineering, nobody works from the same ground truth. Everything is planned on top of "ifs" and "I thinks." The person who actually knows is always in a meeting, on vacation, or just left and the next person has to redo the entire detective work from scratch.

The understanding never accumulates, it just resets. Does anyone actually solve this or do we all just accept the endless rework as normal?