The placebo effect refers to

(a) when an unintended "triple blind" design occurs.
(b) how people’s behavior can change because of their expectations rather than the treatments they receive.
(c) the problems associated with drawing causal conclusions in correlational research.
(d) how researchers can accidentally or unintentionally manipulate other dependent variables.

(B) how people’s behavior can change because of their expectations rather than the treatments they receive.

Example:

A doctor gives a patient a pill with no effects. They told the patient that it would make them happier. The patient thinks that it makes them happier anyway due to the placebo effect.

could you go a bit more in depth with you question? it's quite hard to understand. as soon as you do that i will be glad to : )