Description
The unspoken price of magic, Arcane Fatigue. The use of magic is not as free as people tend to think of. Every cell on a caster's body is placed under pressure by the magical forces that course through the caster's body, at the cast of a spell. Some races have some degree of natural resistance to Arcane Fatigue, but eventually everyone is susceptible to it. The more often a person uses magic and the more powerful the magic is, the more stress their body is placed under. Wizard who study for their magic, learn about Arcane Fatigue early on, but others who obtain magic through other means, often ignore it and fall victims to it. When a caster's body accumulates too much Arcane Fatigue its magical capabilities burn out, becoming unable to use magic anymore.
Consequences
Arcane Fatigue is behind many casters' unwillingness to help societies and people in need, despite their powers. With no clear indication of the fatigue that is piling in one's body, many casters become afraid to use magic frivolously. Arcane Fatigue was the main reason, magical items become popular, in order to preserve caster's lifespans.