Having a positive attitude can be as vital for healing as any drug. Your brain can directly affect how fast you recover from an ailment and how healthy you stay afterward.
Hence the Placebo Effect.
If a patient is convinced beyond all doubt a gelcap filled with sugar will cure them, then it very well may. Of course, most of the time this patient has to be convinced that this gelcap contains a powerful / miracle drug.
In light of the Placebo Effect, you should try to observe the effect of the different treatments or lifestyle changes as objectively as possible. Ideally, you should keep a positive attitude all the time. But, since this is most likely not realistic (not for me at least), you might try rotating psoriasis treatments and see what effect they have over the long run.
It is because of the Placebo Effect that drugs or herbal remedies should be tested with double-blind studies. These are studies in which large numbers of people (with psoriasis for example) take either a placebo or a test-medication at random. The patients must not know which they are taking to maintain the study’s integrity. But the doctors keep track of this and report success if significantly more of the people who took the medication improved beyond those who took the placebo.