“Every one of us believes our own viewpoint to be the best one: such is human nature.” This is not quite how I would put it. Let me, therefore say what I think with respect to this issue.
Whenever I formulate a theory, I believe that my description is ’true’. If I thought that it was ‘false’, I would not write what I write. This is a belief about the status of my description and its relationship to the part of reality I describe. Let us call this the ‘object-level’ belief.
Relative to this, I also have a meta-level belief about my own theories. Do I believe that my theory is ’the truth?’ No, I do not. As a student of the history of the natural sciences, I know that there has no single theory that can claim this status. A better theory has come along and displaced the older theory. This has been the story of scientific progress. I believe that I am doing science. Therefore, I believe that, one day, a better theory will come and displace my own. According to the best criteria of rationality and scientificity we have today, I do think that my theory is better than any others that exist currently in the market place. That is why I defend my theory. It is also my hope that another, better theory will come into being in the near future. If it does happen, I will have succeeded in my aim: because of my theory, a better theory comes into being. That means to say, my labor has been scientific in nature and has contributed to the furthering of human knowledge. That is all what I want: to contribute to human knowledge. However, one needs to remember that my theory can only be displaced by a theory that is better than mine.
In other words, both the object-level belief about my theory (that my description is a ’true’ description) and a meta-level belief about the same (that my description is hypothetical and tentative) are present in me in so far as it is a scientific endeavor, which is human. I want to believe I am both: scientific and human.