Okay, so glyphic. Language of the setting's deities and of magic itself. How'd mortals get their grubby little mitts on it, anyway? How'd the first mages figure out that if you make the right shapes it causes things to occur with no rational explanation?
Well, that's just it. The first bits of the glyphic tongue were figured out by mortals largely via accidents and experimentation. Throw enough symbols out and eventually, you might get one that does something unexpected. But there's only so many that can be found that way - a lot of the more tricky glyphs tend to straight up occlude themselves from the mortal mind in such a way that they can't be found by just coming up with them yourself.
That's where the other method comes in - looking within something that already uses that glyph and it quite literally searing itself into the back of your mind, which causes quite a lot of pain and has been known to drive those with weaker minds absolutely stark raving mad. Lots of early mages who were figuring this stuff out ended up becoming their social group's resident lunatic doing this.
There's also another few bits of knowledge you can get doing this that are a lot more dangerous, collectively known as the Forbidden Truths. These ideas themselves are somewhat sentient and don't exactly like being known, and will generally either make you forget them or try and drive you insane if that's not an option. These are things like the True Origins Of Magic that have been infused with so much mana from the concept's creation that it took on a life of its own. In a metatextual sense, these ideas are the sort where a character is seeing past the fourth wall a little bit.