Imagine the mystery: for its size, the common honey bee should not have been able to fly. At 230 beats per second, its little wings were too small to keep its (relatively) hulking body aloft. Worse: it often transported pollen, thereby increasing its weight. By all accounts, the bee could not fly. Therefore, it didn’t. Right?
Of course not! It took scientists a long time and big advances in technology, but they finally discovered the secret of bee 
flight (among other things, it moves its wings back and forth as well as up and down, which creates more lift; for a great explanation see here). Notice, however, that the bee itself doesn’t know how it flies. It just does. Neither did the scientist know how it flew, but the fact that its flight was mysterious was no reason to discount it.
The same can be said for epistemology. What is knowledge? The question has yet to be satisfactorily answered, and because of this some have despaired of its very existence. What if I don’t know anything? What if I don’t know the real world exists? What if I don’t know the people I love are real? What if I don’t know if I’m real? The questions seem daunting.
The first thing to note is that, like the bee’s ability to fly, the fact that our ability to know is mysterious is not necessarily a reason to doubt that we can know. It may be that, though we don’t know how we do it, we just do. It may be that, though philosophers can’t explain it yet, they will one day figure it out. Of course, there is a big difference in that the bee’s flight is 
empirically observable and so is much harder to doubt. The point here, however, is that our attitudes towards things we can’t explain shouldn’t be automatically skeptical.
So, what should our attitudes be like? Again, we don’t have empirical observation to confirm the existence of knowledge (though empirical observation isn’t necessarily fool-proof), so the non-existence of knowledge is a live option. However, knowing that the mechanisms of some phenomena in the world can be opaque, we should not reject the existence of knowledge unless it can be shown, after thorough investigation, to be impossible. This hasn’t been done. Skeptics have not shown that we can’t know. At best, they have shown that we don’t know how we know. Therefore, as we go forward in epistemology, I’d like to suggest we proceed assuming we know things, though with an open ear towards what the skeptic has to say.