A person who 'works hard' puts in great effort, time, and focus to achieve goals. It implies diligence, persistence, and often long hours. People use it for jobs, school, sports, or any demanding task.
Far and away the best prize that life has to offer is the chance to work hard at work worth doing. Theodore Roosevelt
Life is like art. You have to work hard to keep it simple and still have meaning. Charles de Lint
Surround yourself with people who take their work seriously, but not themselves, those who work hard and play hard. Colin Powell
Whenever I work hard for other people, I always sleep on an empty stomach. Bantu Proverb
For one to succeed in life, one has to work hard. African Proverb
Men in office must work hard. Latin Proverb