I don't understand how the placebo effect is a human bias. Is it?

At least in some instances you could frame it that way: You believe that doctors and medicine are effective at treating disease, so when you are sick and a doctor gives you a bottle of sugar pills and you take them, you now interpret your state through the lens that you should feel better. A bias on how you perceive your condition

That's not all that the placebo effect is. But it's probably the aspect that best fits the framing as bias