the.com/cornerstone
The first stone laid, the one everything else has to apologize to.
means The foundational element on which an entire structure, argument, or institution depends.
from From medieval masonry: the corner stone set first determined the alignment of every wall, so getting it wrong meant rebuilding everything.
Biblical fameThe rejected stone became the cornerstone in scripture.
Time capsulesModern cornerstones often hide documents and dates inside.
Geometry bossTwo walls take their angle from this one block.