I must answer this question because the calligraphy work I’ve been recently copying is the 峄山碑，Yi Mountain Stele, which features the standard official script of the Qin Dynasty.
Among them, the character “世” (shì) is not very easy to write.
This is how “世” is written in the original inscription of the Yi Mountain Stele.
In Xu Shen’s Shuowen Jiezi system, this is a pictophonetic character. It elongates the final stroke of “卉” (huì, originally meaning “thirty” or “plants”), symbolizing thirty years.
When examining even older forms of the character, it seems that this word is related to the pictograph of grass and trees, while also being connected to the concept of “thirty.”
My personal guess is that it uses the flourishing and withering of grass and trees to represent “the alternation of generations,” the original meaning of “世,” and employs “three” and “ten” to signify thirty years.
This is just my personal speculation. I’m not a humanities scholar, so I’m not sure how philologists would view the origin of this character.