Because there are idlers and idlers, who form a contrast.
There’s the one who’s an idler through laziness and weakness of character, through the baseness of his nature; you may, if you think fit, take me for such a one. Then there’s the other idler, the idler truly despite himself, who is gnawed inwardly by a great desire for action, who does nothing because he finds it impossible to do anything since he’s imprisoned in something, so to speak, because he doesn’t have what he would need to be productive, because the inevitability of circumstances is reducing him to this point. Such a person doesn’t always know himself what he could do, but he feels by instinct, I’m good for something, even so! I feel I have a raison d’être! I know that I could be a quite different man! For what then could I be of use, for what could I serve! There’s something within me, so what is it! That’s an entirely different idler; you may, if you think fit, take me for such a one.
In the springtime a bird in a cage knows very well that there’s something he’d be good for; he feels very clearly that there’s something to be done but he can’t do it; what it is he can’t clearly remember, and he has vague ideas and says to himself, ‘the others are building their nests and making their little ones and raising the brood’, and he bangs his head against the bars of his cage. And then the cage stays there and the bird is mad with suffering".
Vincent van Gogh. From the letter to Theo van Gogh. Cuesmes, 22-24 June 1880.