I'm convinced that, if habitual, this stems from how one thinks about their past. As I'm coming to see it, mistakes aren't on equal footing with successes: they, along with periods of no progress, are inevitable but not worth remembering. Lately, as I've reflected back on my life during this ride, I've started picturing it as a series of transparent boxes on a shelf, representing each phase of my life or each major project I've engaged in. Within each box is a series of bright lights, each representing a critical success or peak experience. If it's not one of the lights, then it's not worth dwelling on.
Ideally, I'll always be working on some new box, and not move on until it's lit.