While reading the Harry Potter series, readers are driven to believe that the Sorting Hat sorts students based on their personality traits.
But, there is a theory to disprove this.
Sorting Cases Gone Wrong Edit
When the Sorting Hat sorted Neville into Gryffindor, things were quite strange. Since bravery is the main trait of Gryffindor, you would think one would need it to get in. Wrong! Neville did not possess bravery until he graduated Hogwarts.
Draco and his cronies Edit
A thing one wonders is why Draco and his cronies got into Slytherin. A trait required to get into Slytherin is cunning. But Draco was not cunning. What cunning person would follow Harry Potter? But his cronies were not either. But maybe they just got in because they were not brave (a Gryffindor trait), kind (a Hufflepuff trait), or wise (a Ravenclaw trait).
Student Values Edit
So, why did the Sorting Hat make these decisions? Maybe because it sorts students based on their values, not their traits!