It's not just us keeping them apart. It's everyone in Beszel and everyone in Ul Qoma. Every minute, every day. We're only the last ditch: it's everyone in the cities who does most of the work. It works because you don't blink. That's why unseeing and unsensing are so vital. No one can admit it doesn't work. So if you don't admit it, it does. But if you breach, even if it's not your fault, for more than the shortest time ... you can't come back from that.