1968 D Just Curious. How This Happens?

thank you again !

Imagine you are 1 mm tall and you are standing on the obverse die next to the mintmark. You see this big flat field with a big D stamped down into it. As you look out across the chasm you see a spire of metal coming up out of the depths and ending with a flat surface at the same level as what you are standing on. Now when the die strikes the planchet the metal will be forced down into that chasm. The spire out there forms the hollow center of the D.

Now if that spire breaks off somewhere way down there in that hole and falls away, when the die strikes the planchet the metal will fill that whole big hole, there won't be any spire to form the hollow center of the D and you will end up with a lump that had the outer shape of a D. Just like you see on your coin.