Some people are hard workers, some are not. Some are even slackers. I believe this might largely be immutable. I.e. you can make a slacker work hard, but they'll become deeply unhappy, because it's against their nature, and burn out or quit.

That's why companies pay so much attention when hiring, and are so picky. Managers understand that indiviual output between engineers vary wildly, and try to decide if the person in front of them will actually work hard.