Meanings
main thing, most important thing
„Vielleicht bin ich sogar verrückt. Ich will es nicht in Abrede stellen. Aber wenn ich es bin, so fühle ich mich sehr wohl dabei. Und das ist doch die Hauptsache, nicht?“„Maybe I am even crazy. I don't want to deny it. But if I am, I am feeling very good with it. And that is the most important thing, isn't it?“
main issue
2 more meanings
Conjunction
colloquialas long as, expresses that the following is the most important goal, prioritised over anything else
Er scherte sich nicht um die Folgen, Hauptsache, er bekam sein Geld.He didn't care about the consequences, as long as he got his money.
colloquialat least, most importantly, specifically, expresses gladness about a fact being true even if other things might not be ideal (i.e. Glück im Unglück)
Hauptsache, es geht dir gut.At least / most importantly, you are well / unharmed.