Today when I was learning the glyph origin of 由 (yóu; cause, reason, from), I happened to find out that its actual origin is unknown and that there were many theories out there that try to interpret what 由 could possibly be.
As for the interpretations, the ones I could find are listed below:
The Outlier Linguistics Dictionary of Chinese Characters: Depicts a type of vessel or container.
季旭昇《說文新證》 p.877: Depicts a kind of utensil/implement. (This character is listed under 甾 when I looked it up since it didn't exist in 《說文解字》.)
zi.tools: Depicts a kind of can.
Kanji Networks: Depicts an alcoholic container with a long neck.
Alex Adler, The World of Kanji p.90: Depicts a piece of food entering a mouth.
Wiktionary: Depicts either a container or a helmet. (The helmet theory was later proved to be false as 由 in 冑 was only used as sound component according to 漢語多功能庫.)
These are some of the available theories I could find as according to most of them, this character seemed to depict a type of vessel. However though when I take a look at its ancient form, the resemblance of a vessel doesn't exactly look like it to me.
So if anyone can, it would be appreciated if anyone could help me out with this one and possibly pick the most recent theory!
Also note, I'm aware that this character was most likely phonetically borrowed to mean "cause, reason" and "from".