Some of the most miserable people I've known have been the hardest workers. One example: a friend of mine tried to start a freelance career, but had little experience in the field and rarely reflected on what his clients' needs were. He would work very hard to satisfy his own curiosity about their problems, eschewing deadlines and leaving little time to review his work before delivery. He was among the hardest-working people I've met, yet one of the least accomplished. No one would keep working with him for more than a month.
Correctly identifying which work needs to be done and how is more important than actually working hard. Sisyphean work is not virtuous, no matter how much effort is put forth.