If the wish spell is used to do anything other than duplicate a lower-level spell, then "there is a 33 percent chance that you are unable to cast wish ever again". Does this apply if a non-caster uses a magic item that can cast wish in other ways, such as a fighter using a ring of three wishes?
In other words: If the fighter fails that roll for the first wish and becomes "unable to cast wish ever again", would they be unable to use the other two castings of wish from the ring?
It depends on the specific phrasing of the magic item's description.
Specifically for the Ring of Three Wishes, it says (DMG, p. 193)
While wearing this ring, you can use an action to expend 1 of its 3 charges to cast the wish spell from it. [...]
It is specific that you cast the spell; any consequences of doing so would apply to you. So, for example if you got the "can never cast wish again" on the first try, then the item is now useless to you except as bling.
This is a "specific beats general" situation. In general, a non-caster can't cast spells, but this specific item allows them to cast wish; except as modified (e.g. no material components, since they're casting it from a magic item), normal rules apply.
I haven't looked, but it may be the same for all magic items.
