From: Monte Davis 

black.hole.4.spam{at}gmail.com (Don Hills) wrote:

>First, it allowed the failure to occur in the first
>place (too weak in some areas), and allowed it to land safely (too strong in
>other areas). You wouldn't be as lucky in a current model 737, although you
>wouldn't need to be as the failure would be much less likely to happen.

And of course in the ultimate optimum design, every component is equally strong:

http://www.williamson-labs.com/one-hoss-shay.htm

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