Questions & Answers about Sie lügt nur, wenn sie viel Stress hat.
In this sentence nur means “only” in the sense of “and not in other situations.”
- Sie lügt nur, wenn sie viel Stress hat.
→ She lies only when she has a lot of stress (and not at other times).
It doesn’t mean “just” in a minimizing sense here (like “she’s just lying, no big deal”), but rather restricts the situation in which she lies.
Wenn and wann are not interchangeable:
wenn = when / whenever / if
Used for:- repeated events: Wenn ich müde bin, trinke ich Kaffee.
- general conditions: Wenn es regnet, bleibe ich zu Hause.
wann = when? (question word)
Used for:- direct questions: Wann kommst du?
- indirect questions: Ich weiß nicht, wann er kommt.
In Sie lügt nur, wenn sie viel Stress hat, we have a condition/general case (“whenever she has a lot of stress”), so wenn is correct. Wann here would be wrong.