generation, world, society, public
卋 centers on the broad human span of a generation and the world or society that generation inhabits. The public sense is a natural extension of the shared social world.
卋 is a variant form of 世, which is thought to derive from an ancient pictograph of three leaves on a branch, symbolizing a generation or the passing of time. The modern 卋 shape with 十 over 廿 is a stylized simplification of that older form.
The top 十 looks like a cross or marker, and the bottom 廿 resembles a wide container. Picture a time capsule marked with a cross, holding the memories of a whole generation and its world.
For セイ, imagine a sage (セイ) passing down wisdom from one generation to the next, shaping the world and society.