Say I have a Hat of Wizardry. It allows me to try to cast a cantrip once per long rest. If I use this power and fail my Arcana check (or succeed – it doesn't matter for this), can a friend attune to it, try again, and give the magic item back to me?
I expect that RAI is for that item to be usable only once per day by anyone, but I think that in this case it can be used by several people each day. Am I right, or does something contradict this? I want to know the RAW in this case, but if we know about the designers' intent here, that's useful as well.
Best Answer
Yes, but note that the Hat of Wizardry is unusual in that respect
The text of the Hat of Wizardry gives it the following ability (XGtE, p. 137, bold and italics added):
The prohibition against using the cantrip granting property of the hat is restricted to the particular person who used it (i.e. "you."). If a different person were to attune to the hat (who would also need to be a wizard), they would be able to use this property immediately, regardless of whether or not the hat's previous user had completed a long rest.
Could this be used to get around most time-limited magic items?
No. Nooooooo. No, it couldn't.
The Hat of Wizardry is very unusual in that it relies on a long rest by the user to recharge its utility, and says that specifically that user cannot do so until then. Many magical items require time to be used again, but they often rely on specific times to occur (e.g. dawn) or the use of a finite or renewable resource (e.g. "charges") to use. And more importantly, these other items often cease to work for anyone (not just the current user) until those requirements are met. For example, consider the item Cloak of the Bat (DMG, p. 159, bold added):
Now, if this cloak was used to cast polymorph at midnight, and then attuned to by a new user one hour later (assuming "dawn" happens at 6am), it couldn't be used to cast polymorph again because the "next dawn" hadn't occurred yet. And the cloak doesn't say that only the previous user had to wait: it said that "the cloak can't be used this way again until the next dawn," which would apply to anyone.
As another example, consider the Boots of Speed (DMG, p. 155, bold added):
This is an item, like the Hat of Wizardry, that requires the user to take a long rest to recharge it. However, unlike the Hat of Wizardry, this item would not work for a new user either! It does not say that the boots stop working "for you" (the attuned creature): it says the "magic ceases to function," which would apply to new users as well: and it triggers when the "boots' property has been used for 10 minutes", not when the current user has used them for that amount of time. The DM would have to decide whether it was the previous user or the new one who had to take a long rest to recharge the boots, but regardless, they would not function for a newly attuned user until that long rest had occurred.
So although the Hat of Wizardry could definitely be used to cast unknown cantrips in one day by multiple wizards (once each), note that many other magic items which require time to "recharge" will not be similarly reusable just because someone new attuned to them. You'll need to consider it on an item by item basis.