Hesh is a small village at the bottom of a bluff, north of Coriant. From the bluff, the site of the city of Elwenar is visible: a crater lined with dirty grey glass, in which nothing will grow.
About three thousand years ago (before the elves even brought humans to the world), the destruction of Elwenar shocked everyone sufficiently that mages came together in Hesh and created the Protocols, binding mindspells that prevent anyone from using magic to deliberately do harm to another person. These bindings also include the requirement that nobody may teach magic to anyone not similarly bound. The childhood's end rites and the adulthood rites include preparations for the Protocols, so even someone who discovers their magical power independently and tries to learn out of books is inhibited from doing so without a proper binding from an existing mage.
There are, of course, loopholes. If you don't believe you're doing harm, but in fact are, you can cast the spell. "Harm" means "lasting harm", so a fear spell, for example, can be used in battle or to protect something. Hope at Merrybourne was able to curse her lover Faithful because her geas didn't physically harm him, had an escape clause, and was primarily a restriction on doing something, though because of her malicious intent and her own issues, she did experience splashback.