A diagnosis without knowing the cause is merely a label that creates the illusion of understanding. A comprehensive study in JAMA psychiatry strongly suggests that autism is being significantly over diagnosed [1]. Autism now includes a spectrum of conditions of uncertain similarity because professionals are diagnosing by ticking off symptoms on a checklist. Having certain autistic traits is not the same as autism. This situation can be remedied by replacing symptom surveys with differential diagnosis, i.e., distinguishing a specific condition from others that have similar clinical features.