Decades of JRPG have taught me those seals on ancient evils are almost always made breakable by a dumb kid that has no idea what he's doing.

I really like my friend's justification in his fantasy worldbuilding, which explains it to my satisfaction:

When attempting to seal things of mundane power, mundane objects are sufficient, such as handcuffs and chains. When you try to seal something magically, that extra power needed to seal such a powerful entity has tradeoffs: the more magically unbreakable and irresistible you want the seal to be, the more fragile the conditions holding it must also be. Want to seal all the evils of the world, even for a short time? Well, looks like you're going to need to store them in a top-heavy, ceramic jar with a tiny bottom, like Pandora's Pithos. Trapping a genie? It'll be much easier if you lay the trap with conditions for release, like someone rubbing it three times. Want to bind a violent spirit? Bind it to a fragile mirror, and make it so that she is freed if anyone stares into the mirror and says her name thrice, or if the mirror shatters.

This explains a lot of the folkloric sealing rituals in mythology.

Agreed, but that was the only way we could do it. Sorta like a loophole the genie didn't expect becuz it's so dumb.