In public discourse, narcissism is often portrayed one-sidedly and overly negative, rendering a picture of narcissistic individuals as “toxic people” or “evil characters”. Beyond these salient associations, psychological theories point to a more complex phenomenon, and different developmental mechanisms are being discussed in relation to it. We investigated the prevalence of different implicit theories on narcissism including beliefs about its developmental antecedents. We put forward the question whether grandiose and vulnerable narcissistic behaviors are regarded as congruent or incongruent expressions of underlying feelings and motives, that is whether grandiose behavior is attributed to underlying grandiosity or underlying vulnerability, and vice versa. Results of an online survey (N = 177) show higher agreement with congruent rather than incongruent theories (i.e., grandiose narcissism is attributed to feelings of superiority rather than inferiority, vulnerable narcissism is attributed to inferiority rather than superiority). In line with this, participants displayed predominant beliefs in parental overvaluation as a developmental antecedent of grandiose narcissism/parental coldness as an antecedent of vulnerable narcissism. With higher self-reported prior knowledge of narcissism, endorsement of theories assuming incongruencies increased. The likability of narcissism was not associated with endorsement of the different implicit theories, but instead with perceivers’ own narcissism levels. Results suggest that laypeople employ an “it is what it seems” – heuristic facing both grandiose and vulnerable narcissistic behaviors and are less likely to attribute grandiose or vulnerable behavior to incongruent motivational states. Findings might help to better understand the public image of narcissism and its social consequences.