This only barely glances the number one way I’ve found to work hard: to work for yourself. Working on things other people want is, for me, more difficult than working on things I want. Working at someone else’s company is more difficult than working at my company. With my own company, when things were going relatively well, it was easy to spend every waking minute working. At other companies, putting in overtime is more draining, especially if the reasons for it are because things are late or something broke. I’ve put in a lot of overtime in my life, I tend to work hard, but there’s really no comparison between hard work with a boss and hard work as the boss.
It's the old joke isn't it. A boss is out with one of his employees when they see a Ferrari drive past. The boss turns to his employee and says if you put in the hours and work really hard then one day I'll be able to afford one of those.
In my experience "working for yourself" means in practice "working for your clients." You still need an external party willing to give you money for your work. And they will have requirements about how it is done and when it is delivered that you won't necessarily like
The difference is that you have multiple clients but only one boss. So saying no to a client doesn't mean you lose all your business, but not wanting to do what your boss tells you to means you need to change to a new job.
Very true, being the boss is no panacea in terms of having to do work, it’s usually more work. But the intrinsic motivations really are very different when you are the one on the hook, when you decide which clients to take on, when you are building the company or deciding the dev or research directions, when you decide what happens with the revenue. I mean, for me anyway, but I know it’s true for at least some others too since many books have been written about this. It’s one of the reasons that a mentality of ownership is advocated even when you’re not the boss.