Moment on a rectangular concrete slab

Here is a picture from my engineering textbook. It describes a concrete slab being subjected to normal force $P$ and a certain moment. The moment is expressed by the normal load $P$ affecting at some eccentricity $e$. The supporting reaction is assumed to be linear load. It has been proven that for the slab to be completely compressed along its length $h$, that is, the linear load being negative along the whole length $h$ and $0$ at the left end, the eccentricity $e$ must be less than $frac{h}{6}$.

From this picture, it is stated that the moment attempting to topple the slab over is $frac{Ph}{6}$. This is easy to see. But then it is stated that the moment resisting the toppling over is equal to $frac{Ph}{2}$, and that therefore the factor of safety against the slab toppling over for a slab completely compressed along its length is always more than $3$. How is this possible? How can the moment resisting the toppling over be higher than the moment attempting to topple the slab over and still have equilibrium?