Trauma-focused cognitive behavioural therapy is the form of psychotherapy with the most empirically-based support demonstrating its effectiveness in treating post-traumatic stress disorder. Invasive memories (memories, flashbacks, nightmares) result from conditioning to stimuli (internal and external) present during the event that have been widespread over time. Traumatic event reminders activate the central nervous system because they are perceived as signs of danger and elicit various painful emotional reactions. Avoidance behaviours aim to avoid or escape these reactions, which is reinforcing in the short term because they allow to escape from painful emotional reactions. Unfortunately, these behaviours are counterproductive in the long term because they contribute to maintaining these intrusive thoughts. It is important for the patient to remember that avoiding images or situations reminiscent of the event acts as a factor in maintaining post-traumatic stress disorder (Brillon, 2013, Taylor, 2017). Once the rationale is well explained, the therapist can apply the therapeutic strategies of cognitive behavioural therapy focused on trauma.