Reflection has become a core interest for game designers. However, empirical research into the kinds and causes for reflection within games is scarce. We therefore conducted an online questionnaire where participants (n=101) openly reported perspective-challenging moments within games, their causes, experience, and impact. Where past work has emphasized transformative reflection that changes player's views and behavior outside the game, we found that players report predominantly moments of 'endo'-transformative reflection, which is focused on players' game-related behavior and concepts. We further identify some causes of perspective-challenging moments relating to narrative, game systems, game-external sources, and player expectations. Narrative reveals emerge as a key cause of perspective challenge.