The placebo effect is a scientific fact. Sometimes patients given a "sugar pill" (whether it's a pill, injection, or procedure) will have actual improvement in a medical condition. A placebo is confirmed to improve many medical conditions, not only those linked with psychological problems. [source] Some people think it's even possible to cure diseases like cancer with the power of the mind.
Does human mind have a power to heal almost any disease – the power we're not fully aware of? Or is this power limited?
First some people would get better even if you did nothing, in those cases the the placebo "worked" that is the person got better, but they would have gotten better even without the placebo. The placebo effect "works" best on pain, depression, anxiety, fatigue, while with other cases the person reports feeling better but there was no change in the condition they are being treated for.
Basically they take the placebo, and they think they feel better.