Borderline personality disorder (BPD) is associated with paradoxical trust behaviours, specifically a faster rate of trust growth in the face of trust violations. The current study set out to understand whether attachment style, self-protective beliefs, and feelings of rejection underpin this pattern. Young adults (N=234) played a 15-round trust game in which partner cooperation was varied to create three phases of trust: formation, dissolution, and restoration. Discontinuous growth modelling was employed to observe whether the effect of BPD trait count on trust levels and growth is moderated by fearful or preoccupied attachment style, self-protective beliefs, and feelings of rejection. Results suggest that the slower rate of trust formation associated with BPD trait count was accounted for by feelings of rejection or self-protective beliefs, both of which predicted a slower rate of trust growth. The faster rate of trust growth in response to trust violations associated with BPD trait count was no longer significant after self-protective beliefs were accounted for. Interventions targeting self-protective beliefs and feelings of rejection may address the trust-based interpersonal difficulties associated with BPD.