Irreversibility in the core protocol is a feature, and a necessary one at that. If you start with irreversible payments and you need payments to be reversible

Irreversibility in the core protocol is a feature, and a necessary one at that. If you start with irreversible payments and you need payments to be reversible with some kind of review/appeal process you can add reversibility through escrow. The classic arrangement is a 2-of-3 multi-key system where the payment is made to an escrow address where it can be either finalized or refunded only when at least two key holders concur; the third key, held by a neutral third party, is used to settle disputes when the payer and payee cannot come to an agreement on their own. There are, however, situation were reversible payments are a liability, and there is no way to build an irreversible payment system on top of a reversible one. For example, you can't build a reliable escrow system on top of reversible payments since the payer can trivially circumvent the escrow by unilaterally revoking their payment to the escrow account.