Why is a manhole cover round?

If anyone ever asks you this in an interview, as I’ve had asked of me, they’re probably testing how you think.  I was a bit shocked at first, what does this have to do with code?  Much, as it turns out.  How do you answer this question?  Many of you know the answer, but if you were like me, sadly I did not.  I gave it my best guess.  Reason out loud.  That’s the most important strategy here.  Turns out manhole covers are round so they don’t fall in the hole, and possibly on someone working in the hole.