Yes, transactions are irreversible. If you send Bitcoin to someone by mistake, the only thing to do is to ask him politely to send it back. If you know to whom you sent the bitcoin, which is not a given.

This is why it’s recommended for traders to trade Bitcoin on the same exchange that prioritizes users first, except in the cases where the recipient is a friend you can easily reach out to; if not, then it’s usually not reversible.

This is a strength or a weakness, depending on your point of view.