In reality we are never "fully trained". We are always learning, adjusting to new technologies, new research on education and movement in the field that we are teaching. We are adjusting to the demographics of our classroom and our team we teach with.
I really liked how they talk about redefining the idea of full trained, to something more along the lines of good problem solvers, armed with the tools needed to continue to learn and move forward with new technologies, assessment techniques. and more. We need to support professional development and no longer expect people to come "fully trained" but rather support them as they grow and change along with us.