Principles are ways of successfully dealing with reality to get what you want out of life.
Ray Dalio, one of the world’s most successful investors and entrepreneurs, cites principles as his key to success.
I wrote about key-man risk earlier, which applies the most to those with the largest areas of responsibility, especially the head of an organization. If that's you, then you should designate the people who could replace you and have them do your job for a while so they can be vetted and tested. These results should be documented in a manual that the appropriate people can go to if you should be hit by a bus. If all the key people in the organization do this, you will have a strong "farm team," or at least a clear understanding of vulnerabilities and a plan to deal with them. Remember that a ninja manager is somebody who can sit back and watch beauty happen--i.e., an orchestrator. If you are always trying to hire somebody who is as good as or better than you at your job, that will both free you up to go on to other things and build your succession pipeline.
Beyond that, visualizing your replacement is an enlightening and productive experience. In addition to taking stock of what you are doing and coming up with both bad and good names, you will start to think about how to get your best people into slots that don't yet exist. Knowing that you will have to test them by letting them do your job without interference, you will be motivated to train them properly before the test. And, of course, the stress-testing will help you learn and adapt, which will lead to better results.