Some magic bullets from the past:

• vitamin C for scurvy
• plenty of other vitamins for plenty of other diseases
• clean water for preventing bacterial infections
• washing hands to avoid massive childbirth mortality in hospitals
• bed nets for malaria
• fertilizer for increased crops

If you look how difficult it was to figure out those, and/or how difficult it was to do such tiny changes even while knowledge of it became widespread, I don't find possibility of trivial solution to willpower problem unlikely at all by outside view.

What do you mean by "Amdahl's law"?