To amplify Brian's explanation - before surnames became established in the Island in 16th century, many people were identified by a personal name and a family identifier (similar to in Ireland or Scotland at the time) - O'xxxxx meaning a descendant of a grandfather or better know ancestor (similar to clan membership) or mac Xxxxx meaning son of or ine Xxxxx meaning daughter of. So, in my Killip ancestry there could have been John mac Philip and Jane ine Philip (children of their father Philip) and if Philip was famous or infamous, John's son may have been William mac John or William O'Philip with William's children being known as mac William or ine William or O'Philip.
Probably for tax, inheritance and land ownership reasons the paternal or clan naming changed to family surnames (influence of the Normans). In the Celtic-speaking countries the paternal line was generally taken to create the surname and names such as Macfilip and Macwilliam were adopted for all descendants of Philip or William and ine Xxxx was generally lost.
For some reason (the subject of the posting thread) in the Isle of Man, the Mac- prefix was shortened during the 16th century to create the distinctive Manx surnames such as Killip and Quilliam.
In the earliest manorial rolls of the Island all forms of the above names were recorded, mac, ine, Macxxx, Cxxx, Qxxx and Kxxx -indicating a community in transition - by the creation of parish records in the late 16th century, these names had more-or-less standardised to the modern forms.