Let me tell a second hand anecdote of a Burmese village.
It was a rather small collection of huts raised on tall poles. But it was a village none the less.
All paths in the village were laid out with a connected mass of wood. Along the path were sticks, rising pretty high up in the air. Somewhere along the top of the sticks were a lot of cuts made out in the wood, at various heights. By a knife or so.
In the dry season, this path laid on the ground to be walked on. You didn't have to walk on it of course, since the surrounding dirt was dry.
In the wet season however, floods often came. And so, they raised the path up along the sticks so that it became a water bridge for when floods came. They raised it to the level of the highest cuts that were made in the sticks. A very reasonable thing to do, in order to connect the village in times of crisis, without using boats.
Interestingly, however was the background of the cuts. Each cut represented a water height that had some time ago been the highest the flood had become. So each season, they only raised the water bridge to the level of the worst flood they had experienced.
They did not have a margin.
While they didn't prepare for less than what they had previously seen, they only prepared for the worst flood in history, and not the worst flood in history + a margin.