The first and main point to understand about the Münchhausen trilemma is that it is an argument. As such, its function is to convince other human beings, at least to the extent that they are rational.

The trilemma is an argument about knowledge and for this reason is often misunderstood as proving the impossibility of any knowledge.

This, however, is a logical impossibility. Either the Trilemma is itself knowledge or it isn't. It couldn't possibly be knowledge, however, since if it was, it would be a counterexample to its own assertion.

And if it isn't knowledge, then, why should we care about it?

We need to care because the Trilemma is effective as a rational argument against a certain idea of science as objective knowledge the physical world.

Any idea of science as knowledge of the real world which assumes that subjectivity can and should be entirely left out of science is indeed condemned to an infinite regress. And a good theoretical model of this is indeed the theory of Justified True Belief.

Justified True Belief either leaves you not knowing whether a justified belief is really true, because of the circularity of the theory, or requires that you produce a second-level justification to justify all the elements coming into the initial justification, and then of course to produce a third-level justification to justify all the elements coming into the second-level justification etc., ad infinitum.

Justified True Belief actually describes quite well the history of science, where each generation of scientists produces a new, more detailed justification without being able to say whether the last science is actual knowledge of the real world.

The Trilemma is thus effective against any Justified True Belief view of science as knowledge of the real world. It is effective, however, only to the extent that it is a convincing argument. It is still not, and won't ever be, knowledge.

As a convincing argument, it probably has some effect, up to a point, on how people think about their own practice, scientists in particular.

However, the fact that it is a convincing argument about the absence of knowledge of the real world, in particular scientific knowledge, doesn't say anything at all as to the possibility of knowledge or indeed about whether we know at least some things or not.

Suppose you know X. What the Trilemma says is that you cannot justify that you know X. However, what the Trilemma doesn't do, emphatically, is to prove that you don't know X. Again, the Trilemma is not knowledge and therefore isn't knowledge that you don't know X. It is not even an argument that you don't know X. It is only the argument that you cannot "satisfactorily" justify that you know X. So, if you know X, of course you do, and the Trilemma be damned.

Still, whether you really know X or not is of no interest to anybody but you. What matters to other people is to know themselves whether you know X. However, the Trilemma is this very convincing argument that whatever you will ever say, other people won't be convinced that you know X.

And why should they?