[unethical_ban]

English has many faults, but I am proud of our limited number of cases and (standard) conjugations.

It must be taught since it's a part of the language, but I almost wish non-native German students could skip the "du" tense entirely, if it's that much of a faux pas to use it in the wrong scenario.

[eternauta3k]

So far Duolingo has always taught me to use du, and never Sie...

[wikibob]

Duolingo is a toy for getting a passing familiarity with a language. If you really want to learn it you need to take classes with a real human tutor

[schwank]

Which is exactly what I did coming out of undergrad University here in the US. I started work and then for fun I went and formally studied German at a local college, taught by a native speaker born in Köln. I was educated to use Sie out of respect and only use du with close friends, children, and only when instructed by co-workers and other associates. In my travels I have had many discussions in German and have not once been repremanded, only on occasion told I am fine to use the informal form.