Reflexive pronouns like <em>yourself</em> are used when the subject and the object of the verb are the same person or thing. The antecedent is the person or thing that the reflexive pronoun refers to, which is usually mentioned before.
In the example sentence, the reflexive pronoun is <em>yourself,</em> which means that the antecedent is <em>you:</em>
I do not believe what <u>you </u>did to <u>yourself </u>is for the best.