Helena, without fail you raise some very interesting questions for us to ponder. This is most definitely a useful exercise.
My shopping failures include two second hand items - which I really didn't need but bought because they seemed be be exceptional value (the first two items in Finds). Well they were not good value because I defer to wearing other skirts and coats in my wardrobe that I own and prefer.
Skirt is cute and fits well, but is above the knee and quite cold to wear when working from home in winter, so it gets a pass on cold days and then seems too wintery for warmer days...
Duffle coat - cute in a Paddington Bear way and great for walking Margot on cold non-rainy days, but I generally forget about it and grab my preferred tie waisted coat (also in Finds) that I adore and owned before buying the duffle coat.
Lesson: just because something is cheap and seems good value doesn't mean it should earn a place in my wardrobe - I have to consider whether it fills a legitimate need which clearly both of these items did not.