its an autism thing where you like hyperfocus on the thing i guess. its NOT an obsession, as that's unhealthy.

here's something i copy-pasted from http://autism.wikia.com/wiki/Special_Interests

Autistic people often have an intense and passionate level of focus on things of interest. Some have suggested that these "fixations" are essentially arbitrary and lacking in any real meaning or context; however, researchers note that special interests typically focus on the mechanical (how things work) as opposed to the psychological (how people work).[1]

It is important to note that the special interests are highly important and meaningful to the autistic person, similar to an intense hobby.