I've been flying various models of Piper singles and twins since my first introductory lesson in a Cherokee 140 in 1970 or so. Most of them have an autopilot, and the autopilot has strengths and weaknesses. When I was a check airman in Senecas the FAA required everyone to demonstrate a "coupled" approach, that is, an instrument approach flown by the autopilot. We studied the limitations and regulations (mostly about minimum altitude for autopilot use). And we knew that they were sometimes flaky, so I always told the pilots I was checking "If you do the right thing but it doesn't then you pass."
So I thought I knew the autopilot well.
I had the autopilot in heading mode for the approach brief (hand-flying while briefing an approach makes life too difficult) and went to adjust the heading bug to track the back course. "Hmm," I thought, "in all these years I have never put the autopilot into 'LOC REV' mode." This is supposed to track the backcourse by using reverse sensing.
So I tried it for the first time.
It worked great.
There's always something new to learn.