Many are miserable because they work jobs they despise to afford a lifestyle designed to impress others. True happiness comes from reducing material wants to do work you enjoy, as work constitutes a massive portion of one's waking life. Stop buying things you don't need.
The primary obstacle to achieving one's full potential isn't the fear of failing itself, but the fear of what other people will think about that failure. This external judgment prevents people from taking risks and entering competitive arenas where they could grow and improve.
The "work harder" message is not a universal prescription for success or a call for burnout. It is specifically targeted at individuals who are actively unhappy or complaining about their current situation, offering them a direct path to create change through focused effort.
Happiness stems from self-awareness, which is not about identifying and fixing all your faults. Instead, it's about radically accepting who you are—flaws and all. Obsessing over imperfections and trying to live up to an external standard of perfection is a direct path to misery.