Took my summer bag on a fall camping trip last weekend. Didn't realize how cold it would get at night. Spent the whole night awake and freezing my butt off. Now I double-check the temp rating and bring a thermal liner. Total game changer for staying warm.
Actually, I still find those ratings pretty hit or miss, @lauracooper. I check them too, but half the time a 5-star review just says "great" with no details. Last week I bought a heater with good stars and the instructions were totally wrong.