Therapist drift occurs when clinicians fail to deliver the optimum evidence-based treatment despite having the necessary tools, and is an important factor in why those therapies are commonly less effective than they should be in routine clinical practice. The research into this phenomenon has increased substantially over the past five years. This review considers the growing evidence of therapist drift. The reasons that we fail to implement evidence-based psychotherapies are considered, including our personalities, knowledge, emotions, beliefs, behaviours and social milieus. Finally, ideas are offered regarding how therapist drift might be halted, including a cognitive-behavioural approach for therapists that addresses the cognitions, emotions and behaviours that drive and maintain our avoidance of evidence-based treatments.