Magic has innate ties to the thoughts, feelings, and personality of its users.
One example of personal influence in magic is willpower. When a user wants something, they put energy into the outcome, and this increases its power. Willpower is a catalyst to magical potency, turning a weak or ineffective spell into a powerful spell.
This functions in reverse; performing magic against the user's inner desires weakens a good spell. Healing is one example: if someone attempts to heal someone they harbor ill will towards, it could be counterintuitive and even hurt the person they were trying to heal. Some magic is a result of subconscious feelings and ideas. An aura is largely affected by how who it belongs to. For example, even if their self-image isn't deliberate or consciously known, a user projects this onto their aura. Another example is spells cast by intense focus, thought, or obsession. These are a product of internal feelings, and not actively pursued by the conscious mind.