Yeah, the "it was OK last time" is pretty common, but can get you into trouble... From my stories...
One beautiful summer day, after dropping off the owner at his “cottage”, I was out puttering around in the Cessna 180 floatplane. I decided that some forced approaches, and touch and goes would be good practice. The shoreline waters of Georgian Bay, off Parry Sound would afford me the space and privacy, and the water conditions were perfect! As the story always goes, the first few were just fine…
After another decent landing, I put up the power, and reduced the flap setting from 40 degrees to 20 degrees, which would be my takeoff flap setting. The flap lever had an unusual feel to it as the flap position was reset. Oh well, I was on the step, with the power up, so I was going, and I took off.
Once safely (or so I thought) airborne, I selected the flaps to zero. The flap handle just would not move to a lower setting than 20, and I did not want any more than that! Nothing I could do would retract the flaps. After fussing for a while, I elected to just fly home that way.
I set up a 20 degree flap landing into the bay, and in I went. Once down on the water, I could see that the right flap was trailing at a funny position on the inboard side. I taxied in and tied up.
Examination revealed that the inboard flap track, which is riveted to the rear spar, and upper aft wing skin, had completely come loose. The flap and track were just hanging there….
How lucky was I that the flap had remained in a somewhat correct position for my flight home. If it had suddenly changed position, released, or retracted, the flight would have ended very differently. There is enough lift of a Cessna flap at 20 degrees, that it would be very hard to overcome more than a few degrees of asymmetry.