Run when you will, the story shall be changed.
Apollo flies, and Daphne holds the chase.
The dove pursues the griffin; the mild hind
Makes speed to catch the tiger—bootless speed,
When cowardice pursues and valor flies. (II.i.)

As Helena follows Demetrius and continues to swear her love for him, he responds less than kindly, telling her, “I’ll run from thee and hide me in the brakes” (II.i.). Helena retorts with these lines, observing how her pursuit of Demetrius reverses the usual state of affairs, in which the strong (man) pursues the weak (woman). Helena couches this idea of reversal in a reference to the myth of Apollo and Daphne. This myth involves the virgin nymph Daphne turning into a laurel tree to escape from the lustful god Apollo, who chases after her. Here, however, “Apollo flies, and Daphne holds the chase.”

You do advance your cunning more and more.
When truth kills truth, O devilish holy fray!
These vows are Hermia’s. Will you give her o’er? (III.ii.)

When the fairy enchantment shifts Lysander’s affections from Hermia to Helena, Helena suspects that he, along with Demetrius, is trying to humiliate her with a prank. Lysander’s love for Helena is not a strict reversal, since he did not previously hate her. Nevertheless, Helena understands this turn of events in terms of a negation in which “truth kills truth.” Here, the truth of Lysander’s vow to Helena negates his previous vow to Hermia. This negation has the effect of instigating conflict between Helena and Hermia, thereby reversing their relationship from friends to rivals.

I know you two are rival enemies.
How comes this gentle concord in the world,
That hatred is so far from jealousy
To sleep by hate and fear no enmity? (IV.i.)

Theseus addresses this question to Lysander and Demetrius, who have reconciled their differences. The reversal of rivalry into friendship clearly surprises Theseus, and the duke’s surprise indicates his general failure of imagination. (This failure of imagination returns at the top of Act V, when Theseus refuses to believe the lovers’ account of the previous night.) Despite Theseus’ surprise at the reversal in Lysander and Demetrius’ relationship, the entire play has been orchestrated to anticipate the eventuality of just such a reversal of discord into concord.