"It is demanding on the body and the mind, enough so that strong wizards and sorcerers tend to be frail - so much of their vitality is bound into the act of casting spells that they tend to be physically weaker. Clerics do not suffer as badly, being channels for greater powers - but then, in those cases, they are channeling greater powers, often demanding and jealous ones."

The Duchess pauses, for effect, putting a finger on her chin. "Not to mention the attention of those who wish to use magic. Nobility are not, as a general rule, allowed to be wizards in my world; the mix of temporal power and mystical power is thought to be too much of a temptation." As proven by my Uncle is unspoken.