Let's think together for a minute about how worst-case design really works.
For example, how would you evaluate the safety of the picnic-goers in this picture?
A mathematician might want to calculate the center of gravity of the boulder by measuring the geometrical shape of the boulder, and estimating the distribution of density inside.
Then he would plan to measure the size of the bearing surface touching the ground, and calculate the moment required to tip the boulder sufficiently so that the center of gravity moves beyond the footprint of the bearing surface.
Finally, he would compare the calculated moment to the force of the expected wind, etc.
But would you do it that way? Sure, the mathematical procedure works, but nobody can tell you the exact shape of the boulder (unless you have a really big 3-D digitizer) - and nobody knows what's included inside. Neither do we know exactly how the boulder bears on the ground, or the maximum wind pressure. Since none of the variables are known, our hypothetical mathematician is going to have to make conservative guesses at everything, and as a result I'll bet he concludes that the rock is not safe.
Yet it's been standing for a long, long time.
If it were your job to make the rock safe, you'd probably push on it to see if it moved. Then you'd pour some concrete around the bottom and push on it again until you could push really hard without moving it. That's the way real design sometimes has to work - we make measurements and then correct as needed.
The feedback implicit in the measure-and-correct approach is the way to design efficient structures.

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http://www.neara.org/Moore/balancedrocks.htm
Balance Rock, Lanesborough, Massachusetts
New England Antiquities Research Association
Excerpt from a field report by Jim Moore, "Some Balanced Rocks Across Massachusetts"