No one is an island but you could survive on one (Self reliance)

Mockery and sarcasm cannot pierce the strong armour of the self-reliant person.

These are beaches that no invading force can land on for the self-reliant person is unreachable by comments without merit.
The sharp arrows of insincerity may rain upon them but they will just laugh as the arrows are deflected by the armour of self-confidence and fall harmlessly around them.