Stimming is one of the most commons behaviours associated with autism, having been noted by both Kanner and Asperger in their initial descriptions. While the preferred behaviour varies from person to person, handflapping and whole-body movements are two prominent examples.
There are several theories as to why autistic people like to stim. The first is that stimming is a soothing action by providing a predictable experience despite an unpredictable sensory environment, while more recent theories expand this to include emotions such as anxiety. This is supported by the autistic community who see it as a vital coping mechanism and reject practices which discourage repetitive behaviours as being ‘too autisitic’.