[andersonmvd]

Does it impact your friendship? I'd guess you may resent them if they kept a lot of money, especially when you need the money. Or you may start avoiding them completely when you're aware that you didn't achieve a given goal, no? I guess for small amounts it may work but on the long run it seems like a trap.

[yurishimo]

I just started, so can't really comment on that. So far, it seems fine? We're not talking about life changing amounts of money here; 50 bucks a month at most.

The point for me is to accomplish my goal so I don't have to pay them because I'm a cheapskate.

[MarkVenison]

in my experience (I did pay a few hundred bucks to a friend back in the day) it worked because I felt very bad about giving money like this to someone.