Trading rETH back again for ETH is only possible in the event the staking liquidity pool has ample ETH in it to take care of your trade. This is Rocket Pool's pool of ETH that arises from two resources: There’s heaps https://dev.to/cleopatramorris_d539d19ea/rocket-pool-the-future-of-decentralized-ethereum-stakingintroduction-1m2b