"Sometimes we are right and sometimes we are wrong."
Translation:Foje ni pravas kaj foje ni malpravas.
I'm actually a little torn on how I think that should be handled. On one hand, you're correct that the meaning of the sentence is more or less the same, but on the other hand, perhaps Duolingo should focus on ensuring you know how to translate in ways that are essentially word for word when possible? ("Ni ne pravas" for "We are not right" and "Ni malpravas" for "We are wrong")
I might be wrong here, and this is only my interpretation from looking at the definitions of each word, but ĝusta seems to imply being more factually correct, as in declaring that sodium ignites and dissolves in water. That is a fact and is correct (seriously, look it up on YouTube!). It also means answering a direct question correctly, or factually (as in a teacher asking if sodium ignites in water, and a student responding with yes).
Prava has to do with opinions more so, as in having an opinion that is accepted by most as correct, or having a certain stance in an argument that some other outside person (or later your opposition) considers to be correct.
Prava also implies moral correctnessh; an idea that is a fact, like the sentence "Hitler persecuted Jews," might be ĝusta, but it is not prava because it is morally wrong (at least in most people's eyes, morals being subjective and all).
In the case of this sentence, they seem to be saying that they are sometimes morally right or have correct opinions (and sometimes not), not that they sometimes answer questions factually and sometimes not.