Olivia realising that Peter will be erased from timeline.
Actually, that was Olivia realizing she’s getting Etta back. She says that to Peter in their next scene.
They will create a paradox,observers will never exist so no one is ever gonna save Peter and Walter from the lake. WHAT THE FUCK ?
If the Observers dont exist, then Peter would have been cured by walternate, because September would never have distracted him. And, he would have stayed in Red Verse…OMG… Guess that’s why Peter was a little upset when Olivia told him that the plan will get them their Etta back…