Humans are uniquely capable of imagining impossible and fantastic realities, and pretending to operate within those realities in consistent and coherent ways. Most often, the study of pretence and imagination is limited to children (Fein, 1981; Göncü & Perone, 2005; Nielsen, 2012; Pellegrini & Smith, 1998; Piaget, 2013), but recent scholars argues that adults engage in imaginative pretend play more than previously recognized (Kapitany et al., 2022; Lillard, n.d.; Weisberg, 2015). The cognitive foundations of pretend play were laid out by, Nichols and Stich (2000), and here we apply one of their concepts of pretend play to adults. Specifically, we address their concept of cognitive quarantine - the ability for a pretender to recognize that the imagined events do not influence the real world (and to a lesser extent, that the real world does not influence the imagined; (Leslie, 1987) - and demonstrate that this quarantine is, in fact, porous. We term the process of influence of the imagined on the real (and the real on the imagined) cognitive permeation. We demonstrate that self-reported permeation strongly and uniquely predicts the degree to which novel, idiosyncratic, fictional characters influence our own personal identities.