Here's why:

* Static Friction: When an object is at rest, the friction acting on it is called static friction. Static friction adjusts its force to match the applied force, up to a certain limit (called the maximum static friction).

* Balanced Forces: Since the book remains at rest, the forces acting on it must be balanced. Your 10 N horizontal force is balanced by an equal and opposite 10 N force of static friction.

Let me know if you'd like to explore more about friction!