Ripple, on the other hand, can fail spectacularly with as few as three people. Alice "owes" Bob and Bob "sells" that debt to Charlie, as Charlie trusts Alice. Despite that trust, Alice doesn't feel like paying Charlie, or claims that she never actually owed "Bob", but rather, a hacker made the original transfer and so it never truly existed in the first place.
Its important to make people understand that this is how Ripple works. Charlie made a mistake in trusting Alice, and you making the right decisions about whom to trust is exactly what Ripple is based on. If you have a problem with that, Ripple may not be for you. But understand that this is is not fundamentally different from other trust concerns that are commonplace everywhere ein our lives.
Trust Alice for lunch money, trust Bank of America for your paycheck, maybe trust that Bitcoin won't die a silent death for your retirement fund.
This is particularly true in light of the fact that this:
Charlie is pretty much SOL and can't sue to recover from Alice because legally Alice doesn't owe Charlie anything. His sole remedy is to let Bob know what a jerk of a friend he has.
is just conjecture. A court of law may well decide that a Ripple IOU shall be an enforcable contract. That would be a distinct possibility today, and it will be more likely if people increasingly decide they want to use Ripple.