My interpretation of that has always been something like "repeating the same actions over and over again, but never importing any new knowledge from outside" where "outside knowledge" means books, classes, blog posts, videos, meetups, etc. So you can "learn" to just keep doing the same thing incrementally better by just doing it the way way for 10 years, but to make significant changes, you need whole new models, thoughts, and ways of seeing things.

Now sometimes you may make a big leap purely off introspection, applying logic, empirical experimentation, etc., but that would - IMO - be an exception for most people.