Agnostophobia (from Greek word agnostos, "unknown") is the fear of the unknown. Things that are unknown can be scary because there could be wide range of possible explanations, such as something that are very unpleasant to them. They can be afraid of going to unknown places or even meeting someone who never met or heard of before. Some are worry about the time moving forward as there's many unknown and unexpected events to occur. Sufferers would try to avoid the unknowns as much as they can, until they can be treated by for example psychotherapy or talk therapy.