Suppose that I unconditionally and unambiguously give a person a thing such as a necklace with a moderate value (say $1000): I hand it to them and say "Here, you can have this, I don't need it anymore". Then suppose I have giver's remorse and the next day I request that it be returned. Assuming that the recipient has not relied on the fact of me giving it to them (all they would lose is the necklace), can I revoke the act of giving (so that the courts would order the return of the gift)?

Then, suppose that I intended to give necklace A but mistakenly gave necklace B which I did not intend to give: can I legally reclaim B? In case it's not clear, I am not asking how I can guarantee a take-back right prior to giving the thing, so agreements are irrelevant. As always, relevant citations appreciated.