A couple of analogies might help here.

I can know that there are many languages in the world without being able to understand them all. I can also know that my language expresses some concepts more readily than Spanish and vice versa. Rather than having a key to a single universal language that enables me to unlock the mysteries of each individual example of one, all I can do is speak my own and realise that many people aren't going to be able to understand me without translation. However, the more different languages I make an effort to learn, the more I learn about language itself, coming closer and closer to an understanding of language in general - without ever fully getting there. This would be a subjective approach to the subject of course - a more analytical route would be to study grammar and language in themselves, like Chomsky. But even his field of study doesn't give him an overarching view of language in all its beauty and multifaceted complexity - only being able to speak all languages past and present could get him somewhere close.

Similarly, if someone specialises in biology at university, they can acknowledge that the other sciences are all studying different aspects of the same reality that they are, and that the other scientists' work produces solid results and tangible benefits - all without really understanding that work. And that's before you get to the humanities, all of which analyse the same world as the sciences do, from an even more varied range of perspectives. Rather than being less valid than the insights of the sciences, those of the humanities simply approach their subject matter differently and appeal to different criteria of value.

I'm not a complete relativist - I think a religious mandate to abstain from killing is better than a mandate to kill people when you think they deserve it, and that some philosophical frameworks are richer and more serious-minded than others - but I also don't see the truth as fixed and static, at least insofar as human beings are capable of interacting with it. My view is pretty close to Robert M Pirsig's in Zen and the AoMM and Lila: Quality is the fundamental reality; Quality takes many forms; some things possess more Quality than others but nothing possesses all of it; Quality has both static and dynamic aspects; human thought is at its best when it's partly resting in what it already understands and partly grasping for something currently beyond its reach. This is how all good science, philosophy and theology works.