And that message is actually pretty recent. Before the 20th century you could just go off into the wilderness, build your own house, catch or grow your own food, and then just do whatever you wanted without ever needing money once all of that was taken care of. The work of survival itself was the mental stimulation, and when that work was over you went in search of other stimulation. Nowadays there's a chain of reliance and ownership where you can't settle without purchasing the land, can't build your own house without purchasing the licensing and permits, can't catch your own food without a license or outside of season (and even then you're limited to a certain amount of catch), and need to buy or invest in things deemed necessary to participate in society like cellphones and bank accounts. You can grow your own garden to feed yourself, provided you own the land, but that's limited by seeds you have to buy and whatever regulations apply where you live. Essentially the only stimulation you get is by the excessive amounts of entertainment we have now, because most modern jobs aren't providing anything.

There really needs to be some return to commons where ownership of certain things is just discarded so that everyone has the opportunity for self-reliance and self-actualization without needing to provide something of value for others. Community gardens, city parks, and city pools are like the fuzzy, myopic, "My memory's not as good as it used to be" view of that commons fitting into the modern world. The problem is that kind of participation doesn't provide a verifiable exploitable value the way that working under someone towards a set goal does, and our modern economic systems BSOD at even the thought.

In short, it's okay to not be useful just so long as you have something you want to do. Intellectual stimulation will always be a core need, but working for sustenance doesn't have to be.