What's nice about this scheme, this hierarchical scheme building upwards rather than downwards, is that it allows us to think about illness as well in a somewhat different way. Take a disease like cancer. Since the 1950s, we've tried rather desperately to apply this lock and key model to cancer. We've tried to kill cells using a variety of chemotherapies or targeted therapies, and as most of us know, that's worked. It's worked for diseases like leukemia. It's worked for some forms of breast cancer, but eventually you run to the ceiling of that approach.