With enough cunning and the right tools, the distinction between possible and impossible is a more permeable and more malleable boundary than most perspectives allow for.
There are any number of martial and monastic practices that purport to impart unnatural strength and durability, but the upper limits of training and trickery are still bounded by physics. To exceed them - even a little - requires plenty of both, although there are ancient and arcane means to allow someone to defy them; to do things far above and vastly in excess of the limits of what is humanly possible. Such objects and artefacts and phenomena can even appear to break the conventions of causality, but the conservation of consequences requires effect to follow cause. It is inexorable, a basic principle, perhaps even one of the constants upon which the fundamental functions of our universe are constructed.
A full accounting of the price for ignoring these costs is beyond our current knowing, though payment can be deferred - the aforementioned trickery brought to bear - to create the illusion of absolute freedom from consequence. Effect still follows cause, but there is a certain amount of latitude around when and how these bills come due. Fulcral Brands are one invention, or rather a series of inventions developed in isolated pockets throughout history, that embody this trickery. They allow those who wield them (assuming they are properly prepared and suitably proficient) to, along with other less spectacular examples, turn away steel without spilling a drop of blood and plunge their hands into boiling oil without being burnt.
In either case, Fulcral Brands operates along the same principles. Acting as an interrupting, intermediary vessel, the force of the blows or the heat of the oil can be absorbed, temporarily, into the Brand. Once held, the energy can be consciously and deliberately redirected; the strikes used up all at once to shatter stone or the heat released to instantaneously melt a whole field of heavy snowfall. Such pageantry, acts of showmanship that demonstrate strength without revealing its underlying fragility, are common amongst those who have come to possess Fulcral Brands. Either or both of the absorption and the release of energy can (when performed properly) give the appearance, and confer the consequent stature, of superhuman ability.
Still, the mere possession of Fulcral Brands is not enough to utilise their gifts. They are temperamental and, as such, demand a sympathetic and simpatico temperament from their bearers: A psychological, almost-spiritual steadfastness that acts as the mooring on which the fulcrum is balanced. There are more earnest and exacting traditions in which such meditative placidity and perspective are transformative - even revelatory - but anyone who can even momentarily clear their minds and hearts ought to be able to put Fulcral Brands to limited use. Those who wish to channel more extreme forces through a Brand though, or hold those forces in abeyance for extended periods, need to cultivate more substantial quietude and may find such disciplines helpful.
Almost all designs of Fulcral Brands (varying greatly depending on the prevalent tastes and particular talents of their makers) evince or demonstrate an aspect of symmetry in their construction; a physical expression of their metaphysical purpose. The degree to which this is a decision and not a subconscious impulse, an element every artificer felt compelled to honour in their work, is unclear; with arguments being made that the aesthetic form and function of Fulcral Brands are bound together on a level that transcends intention. Still, even allowing for how little is understood about their physical mechanisms - which differ from Brand to Brand and cannot suffice to account for their effects - there is no real evidence that the symmetry is truly essential.
Regardless of its necessity, the idea or ideal of symmetry is almost perfectly encapsulated in the most famous extant example of a Fulcral Brand, an artefact that has come to be known as the Nin Ùath. A pair of bracelets whose designs are a mirror image of one another, their heavy brass bands are folded around hollow tracks that hold magnetised iron inlays which, when properly aligned, hold the bracelets together as though they were a pair of ornate handcuffs. The edges of each track are decorated with pattern of scoring which (if it is not a coincidental similarity) closely resembles Ogham, an alphabet used to write archaic Irish, though only partial and speculative translations of the markings have been made.
The work of interpreting the decoration is complicated both by the bracelets mirrored forms and the absence of an indication as to in which direction the text should be read, in fact it is unclear whether they represent an early version of Ogham or are, perhaps, an idiomatic code whose cipher is long lost. Other Fulcral Brands are less decorative but more overtly machined, using clockwork or electrical mechanisms to demonstrate a constant whir of uncertain activity, or have been built to obfuscate their function entirely. The more subtle Fulcral Brands are sometimes decorated religious imagery, or even disguised as religious relics or artefacts, so that the apparent miracle of their workings can be attributed to a specific faith or belief.
Given the unanswered questions around how Fulcral Brands work, we cannot be certain that such claims are incorrect: Perhaps the source of their power is belief, if not necessarily belief in an instantiated or anthropomorphised deity? Regardless, the distinction between the unexplained and the miraculous is razor-thin and, if the person using a Fulcral Brand is either earnest or suitably persuasive in their beliefs then witnesses and bystanders might well be convinced that they had seen an act of divine intervention. Remarkable feats can become mythic in the retelling, and if one is minded to think of the use of a Brand as a performative opportunity then it can certainly create or bolster whatever legend one desires.
If the power of Fulcral Brands seems dangerous (or even destabilising) then, it is a concern that is only somewhat tempered by their limitations and, moreover, by the uncertainty surrounding those limitations. Given the duality of their making - partly practical and partly inexplicable - and the current dearth of those who know how to build Fulcral Brands, there is no known method to properly measure their wear and tear nor for them to be maintained or repaired as more common technologies are. As pivots, the unmoving points around which tremendous forces are balanced, they are conduits for incredible amounts of stress, and even the apparently hardiest of Brands eventually falter, fail and break: Typically when such a failure will lead to a horrific (albeit spectacular) death.