Earlier quoted context omitted.
Interesting how you write "Du" and not "du". I'm French and I've been living in Germany for 20 years. I understand and use "du/Sie" more or less appropriately (we have the same dichotomy in French). What I still cannot wrap my head around after all this time is why/when some people use "du/Du", "dein/Dein", "dich/Dich" in writing (to be clear: not at the beginning of a sentence). I guess "Du" is somewhere inbetween "…
"Du" and "du" are generally 100% equivalent. Regular casing-rules apply, e.g. in the beginning of a sentence it's "Du" but inside it's "du". "Kannst du mir helfen?". "Du kannst dir doch selbst helfen!" Sometimes it's written "Du" even if in the middle of the sentence when addressing someone directly. It's technically incorrect, but it's used for emphasis and hence politeness, and that's probably where your feeling co…
That's wrong, it's not technically incorrect. In fact before 2006 the only correct way to address someone personally in written form was to capitalize the Du / Sie / Ihr. Since then you are allowed to write it either way. I still use the capitalized form because I'm old and that's what I learned back in school.