A white shirt that becomes covered entirely with mud is so completely and totally cloaked that no white will show through. Likewise, if your carelessness is entirely to blame for the muddied shirt, it was your fault and no one else's.
The word entirely describes the idea of completeness and wholeness. For instance, someone could be entirely focused on a book they're reading, showing that it has their full attention. A room cleaned entirely has no dust or clutter anywhere, and a story told entirely includes every detail. Something done entirely by one person has been wholly completed by that one person.