Abstract:  Allied militaries have increasingly built out infrastructure, hired personnel and conducted training to refine formal lessons learned processes. However, several recent studies in security scholarship suggest that, for multilateral operations, many collected lessons are never implemented - a phenomenon akin to organizational amnesia. Since existing military learning research has yet to explain the link between formally collected lessons and doctrine, our study answers this question: In multilateral military operations, why do national militaries learn certain lessons from the battlefield but leave other lessons behind? Relevant literatures on military learning (e.g. innovation, transformation) have assessed learning in numerous contexts but not the decision-making stage regarding implementation of lessons into doctrine. We argue that learning officials (i.e. in lessons learned and doctrinal offices) are more likely to implement lessons when trusted internal experts within their professional military networks signal them to do so. To test our argument against competing explanations, we conducted survey-based interviews with 17 military elite officials in the learning and the doctrine offices in four of NATO’s top troop-contributing allies (US, UK, France, Canada) and then employed qualitative content analysis. Our findings reveal that trusted experts have surprising sway over learning officials’ decision-making process - suggesting top-down pressure is insufficient to account for what becomes doctrine and what becomes forgotten. Our research also advances security studies by demonstrating the power that learning officials have in affecting change in the military, and, empirically, our research illustrates numerous lessons from Afghanistan and the justification for why they were adopted or not.