# Is normal reaction a non-central force?

For an object of mass m to topple on a rough inclined plane, we consider the torques due to forces acting on it as shown in this figure:

In the figure, we can see that forces along y-axis are cancelling each other. Hence, net torque about the bottom-right point of box would be, $$\tau = Wsin\theta \frac{h_{box}}{2}$$, which would be non-zero from the beginning of inclination!

But that's not true in practical. So, I thought that "normal reaction" should be a non-central force, which is again not true.

Help me to resolve this paradox.