It's standard to use "falhamos com você" meaning "failed you" (promised you something and did not acomplish, did not attend your expectations).
This is different from "reprovamos você" (failed you at the exams)
In cases like this, where "com" assumes meanings different from "with", normally we use "junto" when we want to say both did the action together: "Nós falhamos junto com você" = "We failed together with you".
You got it! The second option could be "Eu sonho com você" too, but there is a good chance that you get misunderstood.
Duolingo might accept this option, but I really think it shouldn't, because it's important to understand these cases where a preposition take different meanings according to the verb.
pgomes gives a very succinct explanation below when he says "We failed you" means the same as "We let you down", which is a kind of way of accepting responsibility for not living up to a promise or commitment made to another. Although, I would add "to fail someone" is mainly used to emphasize this in the strongest terms. For example, a husband wouldn't say "I failed you" to his wife just because he forgot to stop by the store and get milk. In this case, he would just say sorry, and if he was smart, turn around and head back to the store. However, he might say this to her if he was unfaithful. To fail someone is closely related to "I fall on my sword", which is another phrase we say in English to mean in strong terms you take responsibility for your actions.
:))) funny and really good example :)) thanks a lot for the explanation. BTW, reminds me of the first part of Kung Fu Panda. There, when Master OOgway points at Po as the Dragon warrior, Tigress goes to Master Shifu to say "I'm sorry Master. We failed you." I hope I remember well... but the situation must fit for what you say.
You are doing a test or exam and we decide that you should not pass, thus, we fail you. It can also be that we are not good enough, you have a terminal illness, we fail you as we don't have a treatment that will help, but that's probably not the meaning intended here. If you're a Spanish speaker I think 'te fallamos' is right.
Thanks for the explanation!
I think that perhaps Duolingo should consider adding a sentence or two before or after the one users are asked to interpret to provide some context. Either that, or write a coherent "story" for each module that each question/answer pair would draw from. I guess the main concern with this would be how to do it without incurring a lot of cost that would jeopardize the site's mission to provide language instruction for free.