Why does Thena go crazy in Eternals?

Could you please elaborate on the motivations behind Thena's descent into madness in the film 'Eternals'? What specific triggers or events within the narrative lead her to this extreme emotional state? Additionally, how does this transformation impact the overall narrative and her relationships with her fellow Eternals? Understanding her motivations and the consequences of her actions could provide valuable insight into the complexities of her character and the film as a whole.