Key Lookup isn't applied by default?

I'm trying to learn about covering indexes. In the Northwind database, I select from the table *Categories*: As you can see the table has a non-clustered index on the column *CategoryName*. This SQL query: select CategoryName from Categories where Categories.CategoryName like 'Beverages' returns an execution plan with an index seek: However, this: select CategoryName ,Description from Categories where Categories.CategoryName like 'Beverages' returns this execution plan with an index scan using the primary key index, which isn't expected: I can find the expected behaviour only when I force the query with the non-clustered index: select CategoryName ,Description from Categories with(index(CategoryName)) where Categories.CategoryName like 'Beverages' What is the problem?