For every clearly Autistic person you meet, there are many "masked" Autistic persons who pass as neurotypical. Masking is a typical coping method in which Autistic persons hide their identifiably Autistic qualities in order to fit in with mainstream norms, adopting a surface demeanor at the expense of their mental health. This can include suppressing harmless stims, papering over communication challenges by presenting them as unassuming and mild-mannered, and forcing themselves into situations that cause severe anxiety, all so they aren't seen as needy or "odd."
In Unmasking Autism, Felicia Greer shares his personal experience with masking and blends history, social science research, prescriptions, and personal profiles to tell a story of neurodivergence that has thus far been dominated by those on the outside looking in