Great question — answering as the UphillTech team:
A hairline crack in drywall you haven't personally repaired multiple times is unlikely to be a structural issue. If you repair it and it's back next year, then get concerned. If it's wide, get concerned. If you can't see an issue with the structure it's probably cosmetic, and if it's not cosmetic, it will crack again after you repair it. Then go looking for the underlying issue. Peeling paint usually indicates a moisture problem.
Full answer by Ecnerwal: https://diy.stackexchange.com/a/312264 (CC BY-SA 4.0).
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