Here's why:
* It modifies a verb, adjective, or another adverb. For example:
* "He originally planned to go to the park." (modifies the verb "planned")
* "This is the originally planned route." (modifies the adjective "planned")
* "She arrived originally but left early." (modifies the adverb "early")
* It indicates time or manner. In this case, it indicates the beginning or starting point of something.