An example would be to try and replace the space shuttle with a 747 airplane. It just can't happen. The 747 is the square peg, the space shuttle is the round hole. The 747 cannot replace the space shuttle therefore it won't fit the round hole.
DangerNerd answered Thursday March 10 2011, 4:55 pm: Howdy Jacub,
It simply means what it says: Square pegs don't fit in round holes. So when someone says this, they just mean that whatever they are saying it about doesn't fit in.
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