hindsight is 20-20 (even for a fool); an afterwit is everybody's wit
Proverb meaning that even a foolish person can seem wise after the fact. Used to criticize someone who claims they knew something all along only after it happened.
Saying 'I knew it all along' after a failure is just hindsight being 20-20.
His advice is always after-the-fact wisdom and never helpful.