I actually lived in France for three years and I am using this site to brush up. I'm all for learning how phrases translate from one language to another, but we're not even told beforehand what the equivalent is, and we're left guessing. Not exactly fair for a translation exercise.
Indeed. In fact, "failure" is part of the learning process. Duolingo uses a system of exposure rather than explicit instruction to teach, and therefore actually relies fairly heavily on the learner's ability to absorb correction of errors, as well as their ability to make connections. Users who feel this method is "unfair" should probably consider finding a slow-paced class that focuses on rote memorization.