I have already asked this question.
There are 'penalty' in LN for those who're trying to cheat. But who is The Referee to decide who is a cheater and who is setting up a counterparty as a cheater?
In other word, who or what prove/certify the last LN transaction from A to B was N and not N+1, which B has just dropped in order to set up A as a cheater and therefore steal coins of A as 'penalty'?
You and whoever you are transacting with are both the referees. You keep each other honest. It's explained
here.
a payment on LN is only considered finalized once both payment channel owners have revoked the previous state of the payment channel by handing their partner a breach remedy that invalidates the previous state.
In essence, they can't trick you into spending from an old channel state because you both have to agree on what the current state is.
Also, there's apparently going to be less reliance on this penalty method as Lightning matures. People are already talking about eltoo and achieving the same result without needing penalties.