or, jiang fengmian is a repressed person who projects a lot.
this is a weird, not-quite headcanon, and honestly has more to do with me trying to provide an explanation for the author’s odd choices and getting ahead of myself.
courtesy names (字) are usually given to boys at the age of 15 (known as 束髮之年 in chinese, which literally translates to “age of hair-tying”); but in mdzs, courtesy names don’t seem to follow this rule, especially considering how wei ying (魏嬰) was addressed as “wei wuxian” (魏無羨) or “a-xian” (阿羨) throughout his childhood and teenage years.
the simplest explanation is that the author elected to eschew convention because of artistic license.
but the simple explanations aren’t always the funnest explanations; and i like to consider the doylist perspective when thinking about stories.
currently, i have two interpretations that i favour.
jiang fengmian gave wei ying his courtesy name as a child to signify a brand new identity (i suppose if you want to make a comparison, you could compare it to the moment meng yao became jin guangyao; from a nobody bastard child to not just somebody, but the second heir to the jin sect), to allow him to begin life anew under a name that the head of family personally gave him so as to truly “belong” to lotus pier.
that accounts for why jiang yanli and jiang cheng both call him by his courtesy name, even though they should be familiar enough to address one another by their personal names; as evidenced by how the entire fandom refers to jiang cheng as “jiang cheng” instead of “jiang wanyin”. to wei wuxian, the sage of three poisons will always be jiang cheng, no matter how terrifying or forbidding his demeanour is.
which makes sense, but what about the name “wuxian” (literal translation: no envy, never envious) itself?
we all know that jiang fengmian and yu ziyuan shared an unhappy marriage, and that jiang fengmian resented, or at least disapproved of both yu ziyuan and jiang cheng’s personalities and values, favouring wei ying’s free-spirited heroism over jiang cheng’s dutiful diligence. we also know that the yunmeng jiang sect’s family motto is “achieve the impossible”, and that the jiang sect’s ancestors were adventurous heroes whom travelled across china freely, interfering to protect the weak and needy. and last but not least, we know that wei ying’s parents, who also happen to be jiang fengmian’s servant and rumoured love, ran off together to travel freely and step as heroes whenever necessary.
jiang fengmian’s resentment of yu ziyuan and to a lesser extent, jiang cheng, is slightly more complex than “i was forced into marriage with someone i didn’t love.” jiang fengmian interpreted the jiang sect’s motto very… traditionally, venerating and even idealising the liberty that his ancestors enjoyed (never mind that they most likely settled down for a reason). it wouldn’t be a stretch to say that he envied wei changze and cangsesanren for being able to go off freely, while he had to stay behind at lotus pier because of his duties and obligations as the sect leader. obviously wei changze and cangsesanren didn’t get a happy ending, considering how they both died, but jiang fengmian would have envied their freedom, the fact that they had the autonomy to make their own life choices nonetheless; which is why he clung on to wei ying, the remnant of his lost friends and the lifestyle he so desperately yearned for.
wei ying was his last and only connection to his dead friends, two people whom he both loved and envied, two people whom he shared unequal relationships with. jiang fengmian’s inability to remain true to himself whilst fulfilling his responsibilities as sect leader was what contributed to his unhappy, unfulfilling life; and hence, he bestowed the courtesy name “never envious” upon the only son of his dead friends, in the hopes that wei ying would live a happy and fulfilling life, to compensate for his parents’ untimely deaths and jiang fengmian’s lifelong self-repression.
(we all know how ironic everything turns out to be; history repeats itself, hmm?)
TL;DR jiang fengmian lived his life envying the freedom others enjoyed; he wanted the boy he chose to bring into his family to never experience that pain.
(also slightly-unrelated sidenote, but i think that jiang fengmian’s disapproval of jiang cheng doesn’t just have to do with jiang cheng’s personality, or the fact that jiang cheng is yu ziyuan’s son. there’s more of jiang fengmian than he’d like acknowledge; both of them chose obligation and filial piety over following their hearts - in this way, they both went against the jiang sect’s motto of "achieving the impossible”, choosing to surrender to reality and pragmatism. jiang fengmian doesn’t like to look at jiang cheng, because he sees what he perceives as his own “lack of courage” (quotation marks because i disagree; jiang cheng is one of the gutsiest characters in the whole damn story) reflected in his son and heir.)