The argument for working hard is a selfish one. Slacking off is well and fine. But the reason to work hard is that the skill acquisition curve is exponential. For a very, very long time, you are completely useless—you miss deadlines because you underestimate how little you know, you procrastinate because you don’t even know where to begin. And this feeling is miserable.
The only solution is to accelerate your skills to the point where you get out of this low valley. When that happens, your abilities shoot through the roof. It’s compound interest. More begets more. Skill begets skill. Things become fun. You get to focus on the big picture; you have better ideas; you see the chessboard fifteen moves ahead.
I’m all for working less, but if the goal is to avoid work life misery, skill is the only antidote. For your own well-being, it’s important to work hard.