Pure prediction is only all we need if the total end-to-end process is predicted correctly - otherwise there could be pretty nasty traps (e.g., drug works perfectly for the target disease but does something unexpected elsewhere etc.).
> e.g., drug works perfectly for the target disease but does something unexpected elsewhere etc.
That's very common. It's the reason to test the new drug in petri dish, then rats, then dogs, then humans and if all test passed send it to the pharmacy.
