[dagw]

Making change in person-to-person transactions is a pain. If I owe you $15 bucks and you and I only have 20s, there is no easy solution other than you owning me money, one of us writing off a debt, or me having to put off paying you. Much easier for me to pull out my phone, type in your phone number and the amount I want to give you and just hit send.

[ballenf]

There are network effects. In Germany, everyone has the change on hand because they're using it so much. If they don't someone nearby will have it and be willing to help.