Maybe the first one won't, but the next time they most definitely will. Stealing a phone is one thing, cutting someone's finger is another risk-wise. So if you

Maybe the first one won't, but the next time they most definitely will. Stealing a phone is one thing, cutting someone's finger is another risk-wise. So if you have to dramatically increase the potential penalty for getting caught, you'll make sure it actually works before doing it repeatedly, and this kind of info is shared among thugs