Why did Orpheus lose Eurydice?

Orpheus lost her twice, firstly when she died after being bitten by a snake and secondly when he was leading her from the underworld

• Hades had agreed that Orpheus could have Eurydice back but only

if he walked out of the underworld with her following behind without looking back. But Eurydice tripped and cried out just as they were nearly there, Orpheus turned around, only to see her being dragged back to Hades.