.... I do not consider it a defeat for someone to explore, and see what may be out there.
More like living life. Life has all kinds of cards to deal out.
That said, I would suspect that a lack of applied logic would tend to sidetrack.
Lack of patience, best guess sort of stuff creeps in..... then of course people (myself included) start to see puzzle pieces that seem to fit. So they check it out .... maybe get sidetracked... maybe not.
Doubting, or not really giving the clues an honest effort.... that may be the culprit for many.
Forgetting to give yourself a pep talk every so often .... and give up ...
Probably many things contribute.
Even just getting older.
Life, or parts of it, are only a defeat if one says it is