The gradual increase in responsibility. They have to pay board. A roster for dinners, a bill out into their name (one that you can deal with being cut off for a little bit (!!!).
But ultimately, it is also out habit of just getting it done that means we just do it.
I expect that it is a conversation and agreement of shared tasks and responsibilities.
Cutoff access to wifi and don’t pay phone bills, plenty of ways to get started, but it always starts with a chat.