Plato's cave is a famous allegory about perception and reality. The allegory consists, loosely, of the following:
Imagine a cave with a single entrance. Within this cave sit a group of people who have been born and raised entirely inside and have never left. The sun shines through the entrance of the cave in such a way that passing objects cast a shadow onto the wall - a bird, an animal, a gust of leaves. The group sit on the floor of the cave, and watch the shadows on the wall. Not only do they watch these shadows, but they believe the shadows to be reality and do not believe that any other reality exists outside of it. One day, a member of the group stands up and leaves the cave to see the world beyond. They are unable to interpret reality at first, but slowly come to understand that the reality they perceived before was one of merely shadow.
Now, that may be a slight mangling - Plato includes some oh-so-very whiny bits about the freed cave-dweller returning to the cave and attempting to convince the group of the true reality outside only to be scorned that reads to me a bit like complaining about his critics - but I think this is a very interesting allegory. The cave is often said to represent superficial reality, the shadows on the wall sensory input. The freed prisoner understands that the superficial reality isn't real, and uses knowledge to escape the cave and plumb the depths of truth. The idea is that our perception of reality is fundamentally flawed, and that by empiricism, scientific thinking, and reason, we can "leave the cave".
But I think it's very interesting to think about this concept of "leaving the cave". I'm not entirely convinced that it is possible. I think that perhaps, The Cave Is Inescapable.
Why does this matter? I think that the allegories we tell ourselves about how we think have a powerful affect on that thinking. Believing ourselves to be outside of this cave will affect how we interpret the shadows on the wall. The freed member of the group who strays outside may indeed have more knowledge than the others, and here I am looking at the cave as more of an allegory for perception than one of knowledge. All knowledge is experienced through a subjective lens - through our shadows on the cave - and if we forget that then we risk misinterpreting those shadows.
Rationality, empiricism and solid epistomology are critical tools for navigating the world. These things are the instruments we build to probe the world beyond our cave. The universe itself - as far as we can determine - is a clockwork machine that is solid all the way through. But I believe that it is incorrect to say that we can ever leave this cave. We can only probe outside of it, but the cave - being our subjective experience of the universe - is a container that we cannot seperate ourselves from. If you believe yourself capable of leaving the cave entirely, then I think it is far more likely that you will simply be fooled by some different set of shadows on a different wall. There's no getting out, there's only building better and better ways to probe outside.