There are several reasons why the actual force of friction for an object at rest may be less than the calculated force of friction. One possible reason is that the object may be on a surface that is not completely smooth, and the roughness of the surface may reduce the amount of friction between the object and the surface. Another reason is that the object may be moving slightly even when it is at rest due to factors such as air currents or vibrations, which can also reduce the amount of friction. Finally, the force of friction is also affected by the materials that the object and the surface are made of and the temperature and humidity of the environment. All of these factors can affect the actual amount of friction that is present and may cause it to be less than the calculated force of friction.