I thought I would share one of the canonical heresies in my own campaigns. Obviously, the official books disagree with me!
"Opening the Arts," which requires committing to a very serious Oath, 15 years of servitude, and a Gauntlet, is an Initiation Rite granting access to the Hermetic Arts. Failure of the rite is just failure of the rite, much like for gaining other Supernatural Virtues. At least in my campaign, the Rite also requires time spent studying Artes Liberales (or equivalent Academia), a reasonable magical language, and Magic Theory; but within the bounds of those requirements, anyone can become a magi.
When a maga goes looking for an apprentice, she looks for a youth with symptoms of high intelligence and social maladaptation, tells that youth that he is special and genetically superior to other humans (a form of birth aristocracy separate from the nobility), and then spends 15 years reinforcing it with the corruptive influence of unchecked power, privilege, and cultural norms.
"The Gift" is a theory created by magi to explain why people don't like them despite their excellent social skills, good looks, and charming attitudes; why animals won't obey their every whim; and why people in a position of power mistrust them. Powerful, poorly socialized, self-important, and inempathetic, the resulting magus' belief that "the Gift sabotages social dealings" is only reinforced by the reflexive dislike his behavior engenders in others.
Those few who slip through the cracks and socialize reasonably well are explained away as having a "Gentle Gift," although no mechanism or explanation of how a "gentle" Gift works is provided. It just is, okay?
House Jerbiton, obviously, is wise to the scam and have substantially succeeded in raising fewer spoiled brats.
(I think the behavior of the Founders is the most compelling evidence in this heresy: their brand new Parma Magica theoretically made them immune to the Gift of other magi, but still found ways to rationalize genocide and the destruction of the Others' knowledge... and still required iron-handed enforcement of rules like "don't hurt other magi in the Order" to behave themselves.)