A couple from my recent memory
Flying back home after a day trip oop north, the timing was already tight to get back before SS+30. So I rushed the checks, did a half-hearted run up and took off. I noticed in the cruise that I wasn't making my normal speeds but couldn't see the problem. It was only after I landed that I noticed I'd flown the whole way on 1 magneto. So I was late back, had to use an unapproved NDB approach (which I didn't have a plate for) to find the field, the airfield was shut and had no lights but I landed anyway. Won't do that again in a hurry.
Scud-running. I got caught between rising ground and cloud in a valley once and had a tight turn to get out - I did find another valley to get me back to where I wanted to be but, as a result was rather closer to some houses than the 500ft rule would require.
Each time, a lesson was learned and that's what counts. And not getting caught, of course.
