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.
Evaluate the merits of a past decision based not on what you know now but only on what you could have reasonably known at the time the decision was made. Every decision has pros and cons; you can't evaluate choices in retrospect without the appropriate context. Do this by asking yourself, "What should a quality person have known and done in that situation?" Also, have a deep understanding of the person who made the decision (how they think, the type of person they are, whether they learned from the situation, and so on).