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No, it's a geometry type thing
if manholes and manhole covers were square and a big truck ran over it and cocked it up and turned it on its side it's possible for it to fall in, thus leaving a big dangerous hole
round ones can't do that, it's physically impossible
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I think that's more of an after-the-fact observation, and it's not entirely true. You can make a perfectly square manhole (or any other shape) in which the cover wouldn't be able to fall through. To make the example easy to imagin, here's an extreme:
A (insert shape here) manhole the size of Texas covering a 1-inch diameter hole. The manhole cover can be any shape you want -- it isn't gonna fall through that hole.