For kiddushin (engaged) to work, both sides—the man and the woman—have to opt in and agree to it. We’ll talk in the next Mishnah about a situation where kiddushin happened but was based on a mistaken fact.
The Mishnah says that if a man tells a woman, “Become engaged to me with this cup of wine,” but after she accepts the cup, she opens it and sees that it’s really devash, it’s really honey inside. In another case, the reverse: he tells her, “Become engaged to me with this cup of honey,” and then she opens it and finds that it’s wine inside. The man tells her, “Become engaged to me with this coin that’s made of silver,” and she opens the pouch and sees that it’s made of gold. Or he tells her, “Become engaged to me with this coin of gold,” and then she opens it and finds that it’s silver. The man tells her, “Become engaged to me on the condition that I’m a rich man,” and after the kiddushin was done, she checks his bank account and finds out he’s a poor man. Or he tells her, “Become engaged to me on the condition that I’m a poor man,” and she finds out after the kiddushin that he was a rich man.
In all of these cases, she’s not engaged because she agreed to kiddushin based on a certain condition. Regardless of the outcome, she agreed to something specific. If that specific thing doesn’t happen, then we say that the consent she gave was invalid, and she is not halakhically engaged according to the opinion of Tanna Kamma (first Tanna), even if the mistake is to her advantage. For example, he tells her, “You’re engaged to me with this silver coin,” and she opens it and finds it’s a gold coin, which is much better. Or he tells her that he’s poor, but he ends up being rich. In all of these cases, Tanna Kamma says she’s not engaged because, you never know, maybe she’s in a unique situation: she wanted silver over gold; maybe she had a piece of jewelry that needed another piece of silver. So she specifically agreed to the case of silver. Or she wanted a husband who wasn’t rich. Maybe she wanted a husband who wasn’t focused on business all day, but who was going to give her the attention and time that she so needs.
So therefore, even in a mistake that’s to her benefit, this disagrees with Rav Shimon. He says that if the mistake—the misleading information that he gave her—was to her advantage, where he tells her he has a silver coin but it ends up being gold, or he tells her that he’s poor but ends up being rich, then in all of these situations, Rav Shimon says she is mekudeshet, she is mekudeshet, she is engaged, because we’re going to make the assumption that she would agree to the kiddushin even though she didn’t get exactly what she wanted, but she got better...