That’s great question! From psychological perspective, people like to think that they are right. If they encounter some person or situation that threatens their believes they have three choices:

• accept that they were wrong - might cause some unpleasant emotions, risks being perceived as not trustworthy/knowledgeable
• assume the other party is wrong - the belief is upheld, no negative consequences
• find some condition under which the belief in question does not apply - middle ground Of course, there are many situational and personal qualities that affect how easily person accepts other view as their own.

Eg. if you are self-proclaimed expert on some topic, naturally opinions different than yours are wrong, at least to you. However, if you approach your expertise with attitude of trying to understand underlying principles, it would be easier to accommodate for new, sometimes very surprising facts or theories.

Also, humans are very susceptible to biases, meaning the world they perceive is different to what “objectively” is. One of them is attribution bias, which causes people to assume some results depend on their actions - even if there in no basis for that. This bias started the whole “vaccines cause autism” belief. The reaserch paper which started the whole thing is based on a survey directed to parents of autistic childen asking, do they think autism of their child was caused by a vaccine. It is ridiculous belief for most nowadays, but it provided a clear cause of the disease for those parents.

I know my writing can be confusing sometimes, so let me know if you would like some clarification.