If You Think it, It Will Be...?

I was reading a novel and at one point there was this line:

"When the sweat comes back this summer, 1528, people say, as they did last year, that you won't get it if you don't think about it."
Of course it is reference the plague. The plague that wiped out millions of people in the 16th Century. Millions and millions of people.
When we think about it now, using the above logic seems absolutely ludicrous.

And yet...

There are people nowadays who firmly believe that if you don't think about it, if you don't worry about, if you believe you will not become ill, that you won't become ill. Even further to that, if you put out to the universe only positivity and optimism, that you will never become ill.

I cannot tell you how many times I have been told that I must have somehow put it out to the universe that I deserve to be ill... (Because that's really something everyone who is sick actually does).... and that if I simple BELIEVE that I am healthy, I will be able to cure myself of every ailment I suffer from.

I can only hope that we come to the conclusion of this also being ludicrous before too many people suffer unnecessarily by refusing any kind of treatment beyond this psychological dedication.
Obviously there is a placebo effect - and a placebo effect can be positive. It can even seem miraculous. But for chronic illnesses like many people suffer from, a placebo effect may be temporary or nonexistent.

All I ask is that others stop assuming that if someone is sick with certain chronic illnesses that it's because of 'negative thoughts', 'bad energy', or, intentionally and knowingly, their own fault.