Potential

Potential is a term Kyubey uses in Madoka Magica. While the potential of any given Magical Girl is never explicitly said, Kyubey gives clues and sequences to help estimate the potential of any given girl to become a Magical Girl.

Explanation

In order to become a Magical Girl, a girl in puberty must have a high enough potential.

Kyubey explains that the placement of a girl in her respective standing in the social sphere in the amount of potential a girl has. For example, it states, a girl who is a princess will have more potential than a peasant girl.

Additionally, the amount of potential decides how strong or accurate the wish is. For example, (spoilers for Tart Magica and The Different Story) Lapin made a wish for Isabeau to become human again after becoming a Witch. This, however, did not work as expected. Isabeau's body was a husk, and the Witch took over her body. in The Different Story, however, Madoka makes a wish for Sayaka to "de-witchify". Unlike Isabeau, however, the process worked. It can be assumed that even though both Lapin and Madoka made similar wishes, the potential difference between their potentials affected the strength or "accuracy" of the wish.

Additionally, through a conversation between Mami and Homura, it is stated that the greater potential a girl has, the more powerful a magical girl she will be and, by extent, how powerful her wish can be. This is proved in episode 12 when Madoka became Ultimate Madoka from her wish.

How to affect potential

Warning, this section contains spoilers about the main series and Tart Magica.

In the main series, Kyubey says that Madoka Kaname has massive potential. In the same sequence, however, Kyubey explains that Madoka Kaname was no one special. Kyubey says that, because of Homura's interference, the "strings of fate" has all aligned around Madoka. Because of this, with every new timeline, Madoka's potential power grew greater and greater. As Homura centered the world around Madoka, the potential of Madoka subsequently grew greater. With this information, it can be assumed that if the world or region centers around a single person, the potential of that single person increases greatly. Additionally, it is possible to affect someones potential by making a wish for someone else. For example, Riz Hawkwood wishes that she could form a new, true hero. Thus, Tart could not turn into a witch until she became a true hero. However, it is implied that anyone Riz put faith into (who already had the potential beforehand) would get their potential boosted because of her wish.