I interpret that as don't use X (in this case Docker) with your most essential services. Initially. Get your teeth cut, make some mistakes, establish routines, etc with your internal apps, your low traffic services, etc. Be patient, then once comfortable and confident your start to roll it out to your core, heavily integrated services in production.

Having just come off a year at large(very large) government department that have 100s of core services running in Docker in production, I think the tech is ready, but not sure if every company is ready.