Answer:
For lack of trust.
Step-by-step explanation:
The myth of Orpheus, one of the very few and select mythological heroes that get to descend into Hades and come back to the world of the living, tells the story of how this hero went to the underworld to rescue his wife from death and bring her back to life, a favor that, through his beautiful music, is granted to him. However, there is only one condition, that he does not look back to corroborate if Eurydice is in fact walking behind him, back to the world of the living. He looks back, perhaps worried that she is not behind him, perhaps doubting her and her determination, perhaps doubting the fate that the gods have granted him; and in looking back, she loses her forever.