Rx rotates about the x-axis (in the yz plane), Ry about the y-axis (in the xz plane), and Rz about the z-axis (in the xy plane). We need all three because none

Rx rotates about the x-axis (in the yz plane), Ry about the y-axis (in the xz plane), and Rz about the z-axis (in the xy plane). We need all three because none of them can be made from the other two, but any other rotation can be made from a combination of these three.