They sound the same but work in opposite directions. They both began as Latin terms for stiff and unyielding, but now, they’ve diverged.
A rigid approach is easy to describe, but it’s brittle. Being rigid takes little imagination and a fair amount of fear.
On the other hand, approaching our craft with rigor means that we’re able to eagerly shift in the face of reality. We have rules for ourselves, but one of the rules is to adapt.
Rigor is a combination of expertise, awareness and flexibility. And it’s often in short supply.