Since people seem to really like my vision requirements illustrations, I figured I could elaborate on my theories/headcanons!
Anemo: Purpose.
Anemo users have been unsure or hesitant about how to live their lives or what to do at some point, but all ended up finding something to strive for. Venti found purpose in rebuilding Mondstadt after Decarabian fell, to make the nation a place that the nameless bard would've loved to live in.
Jean found purpose as the Dandelion Knight, Xiao found purpose in serving Morax, Wanderer found purpose in freedom etc. Everyone has something they find fullfilment in.
Geo: Determination.
Geo users have a set path and/or ideal they live by, something they will not budge on no matter what. Zhongli is solid on his contracts, the written word is law and cannot be allowed to go broken, regardless of circumstances. His path is one of mutual agreement and fairness, to ensure everyone and everything gets their due.
Ningguang walks the path of Liyue's pillar, Noelle walks the path of self-improvement, Itto walk the path of acceptance etc. They are determined in their ways and will not bend them.
Electro: Protection.
Electro users all have something/someone they hold dear, and will do anything to ensure it's safety and longevity. Ei loved her sister more than anything else, and would've done anything to keep her safe and alive. Her actions in Inazuma was her terribly misguided way of "protecting" it from erosion, to keep the nation her sister loved so much in prosperity in her place.
Sara wants to protect her people, Keqing wants to protect Liyue's prosperity, Fischl wants to protect her imagination and fantasies etc. They hold things close to their heart and will do anything to protect it.
Dendro: Understanding.
Dendro users are seekers of knowledge and wisdom, wishing to understand the world around them and all that lives in it. Nahida wants to understand people, for wisdom means nothing when it can't be put to practice. People aren't something that can easily be comprehended by textbook knowledge, they must be observed extensively first-hand to even begin to understand.
Baizhu wants to understand the secrets of immortality, Kirara wants to understand human society, Collei wants to understand how to help others etc. They earnestly search for ways to expand their world.
Hydro: Duty.
Hydro users tend to have a strong sense of responsibility and personal principles they live by. We don't know enough about Furina to say for sure what her deal is right now, but I speculate her duty is closely connected to the Heavenly Principles, and that she views herself as Celestia's "executioner" so to speak.
Ayato's duty is to the yashiro commision, Candace's duty is to the desert-dwellers, Childe's duty is to the Tsaritsa etc. They have solid loyalties and set principles they work by.
Pyro: Passion.
Pyro users are full of love and passion for what they do, dedicating themselves whole-heartedly to their chosen field. We know very little about Murata, so it's hard to say what she's like. As the God of War I assume she has a passion for battle? Who knows.
Yoimiya is passionate about fireworks, Bennett is passionate about adventuring, Diluc is passionate about defending Mondstadt etc. They have a profound love of life and what is in it.
Cryo: Contradiction.
Cryo users are at odds with themselves, rife with inner conflicts and clashing desires. The Tsaritsa is described as an archon with no love for her people, and has been noted to have grown cold post-cataclysm. Her harbingers, most notably Childe, say otherwise, though. She's not unloving, but she is disillusioned and vengeful. Her hatred for Teyvat and Celestia is at odds with her love of her people.
Rosaria is conflicted with her lifestyle(s), Ayaka is conflicted with her status and wants, Kaeya is conflicted with his loyalties etc. They are torn by irreconcilable opposites.
