We all can imagine how hard it is to carve four faces in a rock mountain. The measurements have to be the perfect. Even an inch of wrong measurement would lead to disruption of whole project. Every step was to be taken by total precision. Not a single mistake could be afforded after all the efforts.
When they couldn’t fit Jefferson in the monument, whole project stopped. They planned on carving four presidents and now they didn’t have enough space for the fourth one. This was turning into a disaster.
In original plans Thomas Jefferson’s face was placed right from George Washington but later shifted. Why would they do that?