Does the story of Pyramus and Thisbe teach a moral lession or show the origins of good and evil? If so, how?
Ovid's (43 BCE - 17 CE) Pyramus and Thisbe, one of his stories in the collection known as Metamorphosis may not show the origin of good and evil, but certainly exemplifies that actions have consequences. One could argue, perhaps, that the parents' forbidding interaction between them caused their eventual deaths, and therefore their prohibition was evil; even so, the story is lacking in showing the origins of evil, or even exemplifying the good.
If there are enduring moral lessons to be had, the first is that actions and choices have consequences -- the parents chose to prohibit Pyramus and Thisbe to meet; they then chose to sneak away. The assumption (or choice) by Pyramus that the bloodied cloak he discovers upon his arrival at the tomb meant that Thisbe was dead. In his grief, at that discovery, he chooses to commit suicide. Thisbe, finding the dying Pyramus, chooses to die alongside him. Choices and actions have consequences.
The second moral lesson that may be inferred is that the Universe is random -- had the lioness not arrived at the tomb as Thisbe arrived, she would not have left her cloak behind, which set up the tragic cascade of events (had she not left her cloak behind, it would not have been bloodied by the lioness; had Pyramus not found the bloodied cloak, he would not have committed suicide.) It's a bit like the sequence with the dancer being, and not being, hit by the car in the movie Benjamin Button. Events are random.
The moral lessons are enduring -- as the P & T story had been remade by Shakespeare (1564-1616) in Romeo and Juliet (and then spoofed in A Midsummer Night's Dream) and again remade, in our own time, as West Side Story. The theme of "star-cross'd" or "wall-separated" or "wrong neighborhood" lovers sadly seems eternal.