Figure 3.

Top: y and z both simultaneously induce probability mass exclusions in $P\left(X\right)$ leading directly to $P\left(X\right|y,z)$. Middle: y could induce exclusions in $P\left(X\right)$ yielding $P\left(X\right|y)$, and then z could induce exclusions in $P\left(X\right|y)$ leading to $P\left(X\right|y,z)$. Bottom: the same as the middle, only vice versa in y and z.