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.
You should be able to roughly assess someone's abilities after six to twelve months of close contact, numerous tests, and getting in sync. A more confident assessment will probably take about eighteen months. This timeline will of course depend on the job, the person, the amount of contact with them, and how well you get in sync.