The same capital, working in two places at once
Because a liquid staking token is a normal, transferable token rather than a locked position, it can be integrated into other DeFi protocols the same way any other token can. It can be posted as collateral to borrow other assets, deposited into a liquidity pool to earn trading fees, or supplied to a lending market to earn additional interest on top of its base staking yield. None of this requires unstaking anything, the LST itself is what moves through these protocols, while the underlying deposit stays staked and continues earning rewards the entire time.
The practical effect is that the same underlying capital can participate in multiple yield-generating activities simultaneously. A holder isn't choosing between staking yield and DeFi yield anymore, they can potentially get both from a single deposit: the staking rewards embedded in the LST's appreciating value, plus whatever additional yield or utility comes from putting that LST to work in a lending market or liquidity pool. This is the composability liquid staking enables, and it's a direct solution to the opportunity cost problem from the first lesson, capital is no longer forced to sit idle just because it's staked.