Well, exactly, that is in another way, what I am stating: rational self interest is inherently unmeasurable because "rationality" is not something that can be objectively counted. So at any time one should assume that people act in their "self-interest": what at the time they deem "better" (in whatever their will decides is "better" at that point). I am not arguing that people never change or never act wrongly or never do things harmful to themselves. I am arguing that if one wants to "objectivize" their actions then one should assume that their decisions show their interests and their values at each time.