One of the most famous quotes from this play directly concerns the theme of reversals, and the way that there is apparently no rhyme nor reason to the way in which some characters achieve greatness and others have that greatness cruelly stripped from them. These lines are entrusted to Gloucester, who of course himself suffers a massive reversal, as he not only loses his position, but also his sight, and is transformed from a nobleman to a beggar. Note what he says in Act IV scene 1:
As flies to wanton boys are we to the gods
They kill us for their sport.
This simile compares the characters in this play to flies who are being played with by the gods, who resemble cruel boys in the way in which they behave towards the characters. Just as boys are free to taunt, trap and kill the flies that they play with, so too are the characters in this play incredibly vulnerable to the twists of fate and reversals that the gods bring upon them, which is something that Gloucester knew all too well. Note too how this theme of reversal is reflected in the following quote from Edgar in Act V scene 1 after he has delivered the death blow to his step brother:
My name is Edgar, and thy father's son.
The gods are just, and of our pleasant vices
Make instruments to plague us.
It is interesting that Edgar sees the world in a different way from his father, arguing that there is justice in the world, whereas his father, Gloucester, would entirely disagree. However, what is key to note is the way that Edgar's quote reveals his identity and both his and his brother's reversal of fortune, because with the stroke that he delivers to Edmund, Edmund's rise to power ends dramatically, and likewise Edgar's declaring of his identity leads to his rise to power. Reversal is something that nearly all characters experience in this play, and the random way in which it occurs seems to demonstrate the fickle nature of life in this bleak, almost Beckettian setting where what happens to you seems to be detached in any way from your actions.