The phrase 'ipsi sibi nocent' translates to 'they harm themselves' and is an example of reflexive pronouns in Latin, where the action of the verb reflects back upon the subject. In this context, it illustrates how the reflexive pronouns 'ipsi' (they) and 'sibi' (to themselves) work together to indicate that the subjects are both the doers and receivers of the action. This structure is crucial in understanding how reflexive pronouns convey self-directed actions and consequences in Latin grammar.