For a guy from Alabama, "you" is such a simple word. You can be used with your brother, your cousin, your minister, your fishing buddy, your neighbor, some stranger at the gas station, a bank clerk, and even some honky-tonk bartender gal.
In Germany, there's sie and du. There's some German rules on how they are supposed to be used.
Du is for your wife, husband, kids, your best friend, your close neighbor of thirty years, and just plain good buddies. It's never to be over-used, but you can't get a German to note the point of use or non-use.
Sie? It's for everyone else who isn't of a close or friendly nature with you.
A Bama guy will meet up with some stranger at local grill, and chat for sixteen minutes over NCAA football, the weather, some church social, the best beer for hot afternoons, and the best paint for fence posts. By the end of the sixteen minutes....they've exchanged first names and are acquainted. By German rules, in a miracle sort of way.....it's now a 'du' situation. Normally, it would have taken dozens, if not hundreds, of meetings....for this relationship to reach 'du'.
I would imagine that Mark Twain, upon arrival in Germany, fell into a big ditch of issues when handling this sie or du problem. He probably felt that simplicity ought to fall in favor of just one word, and the German reaction was that Germans are anything but simplistic.
So my general advice.....when you feel you've gotten fairly friendly with a neighbor or guy at work....even though it's only been two or three meetings or discussions.....toss in 'du' and they might look a bit shocked that you've elevated them to such a status in just a few meetings. Your response? Well....admit that you would have used 'du' at the end of the first meeting but were a bit slow. Did you break any German protocols? Well.....yeah.....but it's best not to admit that and just keep moving ahead.
Life is awful damn short, and you don't want to waste time on the right German version of 'you' to use.