sinking houses and collapsed retaining wall

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how many collapsed retaining walls have you seen in your life?
http://peretired.blogspot.com/2008/03/retaining-wall-failure.html
(I've seen 2--1 here, and one near my house when I was growing up. I’ve read about more, but I’ve only seen 2.)

how many times have you seen new houses sink to the point where they had to be torn down?
http://peretired.blogspot.com/2008/11/master-builder-strikes-again.html
(not until I got here. Ditto—I’ve read about structures that sink (leaning tower of Pisa), but I haven’t seen them myself)

what does this tell you? It tells me that collapsed retaining walls and sinking new houses are not common occurrences. if they were, then you'd see a LOT more of them. it says to me that properly engineered and properly constructed retaining walls and foundations usually don't fail.
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