Or ego security, perhaps.
(Meijin wa hito wo soshirazu;
“The master speaks not ill of others”)
True masters of their art do not go out of their way to find fault with others. If you are an expert, then you should be free of the insecurity and jealousy that drive some people to drag down, badmouth, or harshly criticize others.
We begin with the particle は (wa) marking our topic of discussion, which is the noun 名人 (meijin), “master,” “expert.” The comment on this topic centers on the verb 謗る (soshiru), “ to criticize,” or by extension “to blame,” “to slander,” “to vilify.” This appears in imperfective form, with negative suffix ず (zu) in conclusive form. Particle を (wo) marks the noun 人 (hito) as the direct object of this verb; bear in mind that while 人 literally means “person” or “people,” by extension it can mean “others,” and that is the meaning it takes here.
Some versions may elide the は; a variant replaces 謗る with 叱る (shikaru), “to scold,” with the same grammar rendering it as 叱らず.
This saying is attributed to our friend the Zhan Guo Ce, a.k.a. the Annals of the Warring States (Japanese 『戦国策』 = Sengokusaku).
(“Sensei wa ichinenjuu bokura no eraa wo kiite, yasashiku oshiete kudasatta. Sasuga, meijin wa hito wo soshirazu ne.”)
[“Our teacher spent the year listening to our errors and gently correcting them. It’s true; a real master really doesn’t speak badly of others.”]