Final answer:
Helena is envious of Hermia because Demetrius loves Hermia, despite Helena's own affections for him. This romantic complexity is a key element in the plot of 'A Midsummer Night's Dream' and shapes Helena's character.
Step-by-step explanation:
Helena is envious of Hermia in Shakespeare's A Midsummer Night's Dream due to Hermia's reciprocated romantic relationship with Demetrius, someone Helena passionately loves but who does not love her in return. Helena's envy is driven by feelings of inferiority and desperation, as she cannot understand what qualities Hermia possesses that she herself lacks, leading her to question her own worth and beauty. This envy is a central theme in the development of her character throughout the play.