It can take a surprisingly long time before we realize we messed something up. Some situations, especially social ones, can look like we're totally killing it...until we look over and see our friends uncomfortably shaking their heads with really wide eyes.
And while we're at it, here's a freebie from experience: If you finish a test an hour early and walk out of it like it was nothing, you're gonna learn the hard way what you missed.
So because our mistakes hit a lot harder when we're not ready for them, here are some signs that a situation's gone sour.