Equivalent exchange is presented as immutable physical law.

The opening narration treats it as axiomatic — Edward and Alphonse pay with their bodies, Winry pays with her hands — yet the system seems to work until it doesn't, and the show never acknowledges the moment it stops working.

Human transmutation breaks the rule first. When Edward attempts to resurrect his mother, the narrative frames this as transgression — not against physics, but against nature, against God — and the violation isn't that input doesn't match output; rather, it's that he tried at all.

The show never shows us the equations failing. It shows us consequence divorced from mechanism. Then the Philosopher's Stone arrives and equivalent exchange becomes optional — the Stone transmutes without exchange, creating matter from nothing, or rather, from human souls, which the show treats as outside the economic system entirely.

This isn't sloppy worldbuilding — this is a culture working through what happens when your resource model breaks. The Stone doesn't violate equivalent exchange. The Stone reveals that equivalent exchange was never the law.