Magic has a life of its own. It can think. Not in as much detail as other, more sentient, species, however. It makes its own decisions and choices, allows only certain people to use it, and makes the people with magic obey it rather than the other way around. It has its own opinions, its own agenda, and its own plans. Similar to a parasite, really.
It is partially connected to physiological state and/or emotions. If the magic user is extremely angry or feels threatened they could, completely unintentionally, release a burst of magic energy, because their survival instincts tell them to destroy the enemy/threat. This only happens in some cases. The more emotionally stable a person is, the more stable their magic is, and vice-versa.
Magic in people
Potentially, there is so much magic can do, but not as much that it wants people to be able to do. This means that it’s impossible to learn it all, especially since magic is stronger that other creatures. There are magical artifacts that it doesn’t want people to see or understand, and these artifacts themselves are magic and also want to control people’s minds. Some magic is more controlling than others and there are those that would possess someone completely given the chance. This kind of magic is bound to things like books, and can only control those who read it or try to learn the magic itself.
Once someone has magic, the magic can’t leave. It will only do what is its best interest, rather than the host’s. Luckily, magic dies with the person who has magic and it never wants to die.
Some species handle magic better than others, and humans aren’t one of them, which is why humans with magic are so uncommon. It’s much more suited to naturally magical species because their biology is almost hardwired to be able to accept it. Typically, the magic will choose something that can survive it, without dying or going insane.
The magic must also choose someone before their brain fully develops, to make sure their influence is deep rooted and they can partially influence the kind of traits the person develops. The age that the brain develops fully at varies between species.
Magic in the world
Magic is almost everywhere in the world and often, the landscape is more magical than the creatures living in it.
To learn magic means to better understand it, and that, in turn, means to better control it. Theoretically, anyone with a magic essence can learn any magic, bit in practiced, this is not the case. Magic is learned the same way as any other skill, like learning to read. If you imagine that everyone in the world is blind and the magic people just have rather bad eyesight. It’s a skill that only certain people can learn, and even then it’s extremely difficult, because the magic doesn’t want you to control it.
The books that exist now are mainly the most dangerous ones, as they are the only ones that needed to be kept sealed away in books. Reading the books could kill a non-magic user and start trying to control the magic users who open their books.
Trying to resist them of even just opening the book damages people and attempting to decipher too much of its contents at once can cause serious damage to the Frontal and Temporal lobes of the brain. This much exposure to raw, powerful, magic can cause permanent brain damage.
Minor effects will include nosebleeds and headaches while the more serious effects can be comas, shock, the magic gaining full control or even death in some cases.
Often the books are written in an unusual language, which on its own would be difficult to decipher. This only adds to the problems.
Limitations to magic
As stated above, people can only learn what their magic wants them to learn. There are limits; boundaries that people should not –or in many cases, cannot- cross. Since it’s near impossible to control, it poses a constant threat to the user and people around them.
I also said before: “The more emotionally stable a person is, the more stable their magic is, and vice-versa.” This can cause problems for people because simply finding out that they have magic (Or, to be clear, a brain parasite that wants to posses them and gives them the ability to accidentally kill a loved at any moment) can be a traumatic experience for some. It could cause identity crisis’ or something similar. Having depression, a anger issues or and Anxiety disorder (especially in people prone to panic attacks) can be dangerous for everyone.
People with magic must be relatively emotionally stable for the magic to choose them, and if brain damage or psychological issued develop later in life, there would be nothing that the magic to do to help.
The more powerful a person’s magic is, the more powerful the side effects are. Its more about a person’s ability to deal with what they have that how much they have.