Here's why:

* Magnetic field lines: Magnetic fields are visualized using lines of force that originate from the north pole and terminate at the south pole. These lines are densest at the poles, indicating a stronger magnetic field.

* Magnetic flux density: The strength of a magnetic field is measured by magnetic flux density, which is highest at the poles.

* Concentration of magnetic energy: The magnetic energy is concentrated at the poles, leading to a stronger force.

So, if you want to maximize the pulling power of a magnet, you should place the object you want to attract as close as possible to its poles.