For the prisoners in the cave, the shadows moving across the wall are their reality. There is nothing else for them to see, they have no knowledge of the world awaiting them outside. They are content in their ignorance; they have no desire to expand their worldview because their present situation is all they know. As Plato says, "the truth would be literally nothing but the shadows of the images." When a prisoner is released, his entire world is shifted. He yearns for the comfort of his previous reality; he shies away from the truth of real objects in the sunlight. The sun blinds him, so he is initially unable to see what his instructor tells him is reality, and is confused when he is told that the shadows he once saw, his old reality, are only an illusion cast upon the cave wall. Eventually, he becomes accustomed to the outside world and its truth, and pities the prisoners in the cave who see themselves as lords over the shadows, "conferring honours" amongst themselves based on who can pick out the shapes the fastest, and who can tell which one will come next, etc. Their honors are empty because they are seeing nothing, and only the escaped prisoner understands that. Yet when he returns his eyes can't see in the darkness, as adjusted to the sun as they are, and it is the prisoners who see him as the wrong one because he can no longer see reality as they do, and they fear that kind of fate; they condemn it.
Based on this reading, it would seem that while reality is the state in which we live, our mindset and what we believe, truth is how things really are, and can only be seen when we put aside ignorance and embrace it. We can choose to escape truth by changing our realities, and we can trap ourselves in a certain reality by choosing to ignore truth. In the same way we fear things we do not understand, we may initially reject truth for the familiar comfort of our old reality, but in the light of truth reality changes.