Why would I want to quantify it? The burden of proof is on the thief. I have a gadget that will, with some probability, steal your life's savings. It operates

Why would I want to quantify it? The burden of proof is on the thief. I have a gadget that will, with some probability, steal your life's savings. It operates through a process that is analogous to a human chewing. When engineering it, we just say for simplicity that the gadget "chews". Of course, that's only a metaphor -- machines can't chew. But (and here's where your argument gets ridiculous), unless you can quantify the fact that my gadget can't chew, then I will steal your savings. Good luck.