Maybe we should work on that presupposition first. If we're talking about career and material success it's probably true, but these very rarely bring true lasting happiness. You also have to look at who's telling you to "work hard" and why it's in their interest for you to do so.
Imho once you go above a very low threshold of income (allowing you to live comfortably without excesses) you should have better things to do with your time than spending 7+ hours a day working.
Vacations are the proverbial carrot on a stick. "Be a good worker this week and you'll get to spend your money and enjoy yourself this weekend", "be a good worker this quarter and you'll get to spend your money and enjoy yourself during the next vacations", "Be a good worker all your life and you'll get to spend your money and enjoy yourself during retirement". Fast forward 45 years and you spend literally 70% of your life either working or sleeping, the rest being divided between distraction that barely keeps you going (daily Netflix or video game, weekly party, quarterly vacations) and chores. You're now physically and mentally a shadow of your past self but you have all the time you want, success!
It's extremely easy to get lost in all the little made up games we play days after days and miss the big picture.