How Do You Know if You Don't Want to Do a Stun in a Movie?

I live with Chris McQuarrie and Tom Cruise and I come back every evening from filming. The way that Chris and Tom work is they're constantly learning about what's possible to do in these action sequences safely for real. So nothing is sort of set in stone. It's this fluid discussion and this process of discovery because no one has ever done anything like this in any movie ever before and probably never will again. But still it's amazing to have a ringside seat to that.