"Why are you not taking a bag?"
Translation:Dlaczego nie bierzesz torby?
It's also very similar in some non-Slavic languages especially Romance, like French 'pourquoi/parce que', Italian 'perche' etc.
To return a favour - Your зачем is a false friend of our 'za czym=po co' ('Зачем ты идёшь в магазин' looks for me like 'What are you going to the store for'). So the mechanism is lookin almost the same from the other side ;)
Sorry, I thought You are a Russian native.
But to tell the truth, I learned a lot about my language since this course started ;)
Yes. But it is so popular, that actually it often seems more (or at least equally) natural than "torba". That's why we decided to make it a starred answer as well.