“And now, you have a situation where each one thinks the other is wrong, while in reality, it is entirely possible that they are both correct for their own personal circumstances. Isn’t that possible?”
Yes. But it is also possible that each one of their reasoning applies to each others circumstances just fine, and they simply have different ways of viewing the reality. That’s how Gd made it work, people think differently. So from each perspective, the other is wrong, and to say “for him its fine” is a sign of a weak intellect – as the quote from Mr Nash that I wrote.
Ditto for your second remark. According to what I’m explaining, always taking the view that “Different things work for different people” is equivalent to not really having a view.