I'd have to say that one thing I definitey have learned as a CFI is that complacency will definitely get you into trouble.
I consciously perk up during critical phases of flight especially at the end of a 12-16 hour day since I know I'm exhausted.
The worst is when you're flying in an aircraft you're unfamiliar with. For example, yesterday I began training an instrument student in his Liberty XL2. Pretty nice plane, but definitely one I'd be a little screwed in if there was an engine fire on start up since I havent had the opportunity to sit in it and soak in all the locations for stuff. Of course after the flight he said that I could take it anytime I want to take my g/f out for dinner. Nice offer but definitely not something I want to do until I'm more familiar with it.
As for war stories - I've had about a dozen almost pukers (greenies) but always gotten down in time.
I've almost been off the runway a few times, but always brought it back.
I've been spun a lot, but always seen that coming, the most interesting was right on the border of a spin turning base to final in a slip with bottom rudder (sound familiar???).
I've had a few
very hard landings.
I had 1 engine fire on start up in a carburated engine that was over primed (no damage other than plastic melting) - that was exciting.
I had to land once in a 30 gusting to 40ish direct crosswind in a aircraft with a 15 kt capability. That was not fun.
Need some more?