Every entity in Wikidata is implicitly an instance of (P31) entity (Q35120). These implicit instance of (P31) statements are not all observable in Wikidata. In general no item should explicitly be an instance of (P31) entity (Q35120). Only a small predefined set of items should be subclasses of (P279) of entity. For any regular entity the implicit relationship suffices even if there is no other class that can be found for the entity to be an instance of (P31).