And there may be other obstacles. My favourite is the following.
The Sundering is shrouded in mystery. That's because the magi who attacked Tremere were masters of pre-hermetic mind magics. Those magics linger as of today, and among other things explain why House Tremere makes certain 'strategic choices' described in HoH:TL that are, at any close inspection, utterly irrational; the magic of the Sundering is responsible for those choices, and for keeping them out of Tremere scrutiny.
One of these dumb choices may have been the Schism War. Another is certainly the choice of Tremere duelists to have their Twines - to specialize in two Forms and two Techniques, so that (we read in HoH:TL) they may always have a strong Art if the other is vetoed, whether they are the challenging or the challenged party. This is obviously foolish, because one strong Art and one very weak Art provides little leverage to the Tremere focus ... and it ensures that the Tremere duelists can be kept in check by the Thirteen Guardians.
The latter are a mysterious cabal of thirteen magi, traditionally one per Tribunal and one per House (except for Tremere, whose responsibility was taken by a descendendant of Trianoma - exactly who carries the burden of Diedne after the Schism is left to the individual troupe). Each Guardian specializes in exactly one Technique and two Forms, distributed in such a way that for any possible set of Twines there are always at least two nemeses, i.e. Guardians whose Technique matches one of the Twines and whose Forms match neither. The Guardians keep tabs on the strengths of the various Tremere duelists; whenever one is abusing Certamen, one of his nemeses appears to champion the opposing cause.. As the (champion of the) challenged party, he can choose the Form - one in which he is strong, and the Tremere weaker, even with the advantage of the Tremere Focus. The Tremere chooses a Technique, but the nemesis through his veto can ensure that either both duelists are strong, or both are weak in it.
Thus a Tremere dueling his nemesis can only bring to bear two weak Arts against a strong and a weak one, or a strong and a weak Art against two strong ones. The fact that Guardians specialize only in three Arts rather than four increases their advantage further, and they usually win even against opponents of somewhat greater seniority - not always of course, but enough to keep the Tremere in check. The magic of the Sundering (and the fact that guardians tend to operate discreetly) keeps the Tremere from noticing this systematic opposition.
Minor Flaw: Guardian (Story, Hermetic)
You are one of the Guardians, the thirteen magi of other Houses tasked with keeping Tremere certamen in check. Choose a Technique and two Forms, in which you should spend all your starting Art xps and you are expected to specialize. You have access to excellent books in these Arts, and any other Ability used in Certamen (anything that can be bought with 'standard' Covenant points); however, you must keep their existence secret, just as any other aspect of your affiliation. You also have the equivalent of a Free Secret Vis Source in each of the two Forms, though you can only use it in Certamens you fight for the Guardians. You gain a free xp per year since you started your apprenticeship in Order of Hermes Lore (certamen). And you can call on the help of your fellows.
On the flip side, you must keep track of who's who in your Tribunal (and in the Order at large). You will never have a Reputation as a magus of magical or duelling puissance, thanks to the Sundering magics (then again, this can also be a boon). But you will be called to fight duels, often in other Tribunals, for causes that are not yours and may even be antagonistic to yours. If you have no means to travel quickly, it will be provided to you. Win or lose, your role will soon be forgotten. Eventually, as you grow into the senior ranks of the Guardians, you will be tasked with coordinating their activities.
Hermetic Puzzle: Prove that thirteen Guardians are necessary and sufficient to ensure that any set of Twines has at least two nemeses!