In response to the dynamic and complex corporate environments characterized by intensified competition and evolving consumer demands, the call to open up the strategy process is on the rise. Organizations increasingly realize that the potential for valuable ideas can also originate externally, beyond the confines of the organization itself or from internals that are usually not involved in the strategy process. Yet, openness is not universally applicable due to inherent challenges in finding the right levels of transparency, inclusion, or participation among others. In tackling the puzzle of why and how companies embrace openness in strategy-making, this research identifies a number motivational and inhibiting factors during the transition from a closed to open strategy and develops propositions to inspire future research. We address this prevailing issue by conducting an in-depth longitudinal single case study centered around an incumbent from the European energy industry. Our approach involves case interviews and the special format of open strategy workshops with 13 industry partners to identify why incumbents really struggle to implement an open strategy initiative. In addition, ways how to leverage barriers and inhibiting factors to develop a fruitful open strategy process are presented. We conclude with promising hints for senior strategists of incumbents supportive for their transition towards open strategizing.