The twenty-first arcanum is about betraying the place and the community a person belonged to. Denunciation, going over to the side of those who came with war, giving up one's own for the sake of one's own safety.
The descendant feels this as rootlessness. Nowhere do they truly become one of the place: neither where they were born nor where they moved to; there is a pull to change place, and after the move the feeling comes back. There is often a family story about which nothing is known except that "grandfather did something of that sort", with no details.
The working-off is to serve the place where you live. Not in the grand sense but in the plain one: to do something useful for the people nearby, where you are standing now. And not to gain at the expense of your own — this law is first of all about the choice of whom to give up in order to survive.