We all have our own idiosyncrasies and habits which we learn mostly from personal experience. Formulating a useful mental model of the world is what’s kept our species alive over evolutionary time. If eating a particular plant made you ill, then you knew to avoid it in the future. The problem with this is that our personal experience is very susceptible to error. I strongly dislike cider and even the smell turns me away. The reason is that when I was about sixteen I got very, very drunk on scrumpy and the aftermath is not something I want to remember. I hate cider to this day but there are many who love the stuff and it does them no harm (within limits).
The personal experience effect, otherwise known as subjectivism, works in both a negative and positive sense. Getting fed up with the symptoms of a cold you take a heavy dose of vitamin-C and within a couple of days everything is back to normal. The chances are that things would have got back on track without the vitamin-C as colds only last for a finite time anyway. Now however, you’ve associated vitamin-C with curing the common cold and nothing will change your mind.
I suffer from osteoarthritis and I’ve heard no end of accounts of treatments from rhubarb leaves to fish oil. There are those who swear by these treatments but then another problem arises. Some claim fruit juice eases the symptoms of osteoarthritis and others claim the acids in fruit juice exacerbate the symptoms. Both sides firmly defend their conflicting positions while there is actually no evidence for either claim.
I have encountered some who take their own subjectivity to extreme lengths. I came across someone who claimed all modern medicine was a conspiracy by big Pharma and governments to poison a gullible populace for profit. This sounds delusional, but it turned out he had seen his Grandfather die after suffering from cancer and the effects of chemotherapy. His very strong emotional experience had a profound effect and no amount of reason or fact would ever have the same impact.
There are those who offer their well-meaning subjective advice to others and there are those who tell their own anecdotes of how vitamin-C cured their cold. I might disagree and challenge their views but it’s a human trait and so I’m careful not to make the arguments too personal. Then there are the quacks that offer wonder cures for serious disease to those willing to pay them enough money to reveal the secrets “that medicine doesn’t want you to know.” These are the charlatans, the shameless exploiters and they should be treated the same as any other con-merchant. Those are the ones that need the blunt end of verbal wrath but just remember there are also victims of the charlatans where we should be more empathetic.