When information is remembered or accessed, several measures attempt to tap the phenomenology of that experience (e.g., feeling of knowing, remember/know). But, what about retrieval failures? I'll be presenting a novel and parsimonious method for examining the extent to which individuals can discriminate between what is not available and what is merely inaccessible in their knowledge bases. We first examined this type of metamemory in both younger and older adults and with a wide range of general knowledge difficulty. Current work, funded by an NSF CAREER Award, focuses furthering the theoretical understanding of retrieval failure experiences and ultimately, developing ways to stabilize access to prior knowledge across the lifespan, alongside teaching initiatives that bring this research to older and younger adults together in the classroom.