Lots of little mistakes mentioned. But there are big mistakes that are by far most dangerous, and kill more pilots.
Number one: trying to turn back to the airfield with engine trouble when TOO LOW. And of course too low to recover from the spin that is the consequence.
(Always have a plan B in mind before you take off)
Number two: pressing on to planned destination when the weather is getting worse.....Never be ashamed to return to base, don't worry what anyone else will think of that sensible decision.
Fatigue. Under pressure. Don't be afraid to say no. I found a useful phrase to be "These conditions are over my personal limitations."