> Shouldn't we expect some small percentage of failures Yes, and this is really solved at a more local level. Doctors aren't prescribing new drugs like candy.

> Shouldn't we expect some small percentage of failures Yes, and this is really solved at a more local level. Doctors aren't prescribing new drugs like candy. They, too, are skeptical of their success and will reserve those prescriptions for the most desperate cases. Over years, we (and the doctors) learn how effective these drugs are and what potential side effects they have.