Trump says he is taking hydroxychloroquine because it is a good idea. It seems promising and there is minimal downside.
But it is said - in set theory apparently - that there are a great number of reasonable explanations for any given set of facts. Presumably only one of those reasonable explanations will be true or correct. So the probability that any one reasonable explanation is in fact the true or correct one is close to zero. One correct reasonable explanation and a great many not-correct reasonable explanations.
That appears to be why almost all good ideas in medicine are wrong. And in every other field as well.
The corollary is well known. Thoroughly test each good idea before accepting it. Double blinded randomised trials are the gold standard in medicine. The FDA and similar organisations require convincing trials before releasing any 'good idea' on the public.
It is not a good idea to accept even very good ideas till they have been thoroughly tested. Good ideas are usually wrong.