It has to be difficult because it took the demolition of Logical Positivism to get to it. The hard part, historically, has been admitting that our sense of uniformity is an assumption and not some form of knowledge itself that can be acquired or tested.
Hume pointed this out very clearly, but the deduction got no purchase -- it was seen as a combination of nihilism and blind faith, and it was an argument substituting necessity for uniformity. But our sense of necessity is a presumption of uniformity itself. What if the overall rule is good, and this instance is flawed?
Kant took Hume seriously, but then addressed the problem with a distinction that lacked a difference, proposing 'noumena', a basic reality that had rules of its own, that were only partially detectable in phenomena, and much of philosophy was satisfied with that answer or some simple parallel.
Quine (and to a lesser degree Wittgenstein before him) eventually got back behind Hume's problem and realized that this is a bias that cannot be tested, not just in the sense that we cannot prove it, but that if we pursue it to its logical end, it falls apart on its own. It is necessary to our thinking to presume that simplification is what makes ideas possible. But how would we know? We only have our ideas, and we all started with this bias to begin with.
If uniformities can force themselves upon us without our coming to them ready formed to accept them (or to make them up, when we can't accept the facts without them), then we do not have the assumption of their existence we have some natural sense of their objective existence. That possibility appeals to us so much that it is an obvious basis behind all of our science, and before that, behind all of Western religion. (There is a very good argument, from Whitehead, that the West got to science first not because of our philosophy, but because monotheism, with a focus on unity, enshrines uniformity above other aspects of logic.)
But we know that science occasionally discards large parts of its basis, and we have seen the departure from Orthodoxy and the logic of Protestantism take apart and reconstitute our religion very effectively, maintaining its purpose throughout. We find these things hard to take, and almost impossible to incorporate into a functioning philosophical outlook that is not nihilistic to the point of being unproductive. Instead of some deeper form of fluid-yet-stable belief that the data calls for, we end up with modern post-modernism which oversimplifies as a matter of course because it feels like there is no reason not to.
(I am purposely not referencing this because I think it is a homework assignment, and if you want to reconstitute this argument, you need to find these references for yourself.)