According to numerous studies summarized in The Newsletter of The American Institute of Stress, not realistically knowing ourselves and our limitations can lead to much stress, frustration and unhappiness. Those who do not learn from their past mistakes and behavior patterns are doomed to repeat their mistakes.
For instance, numerous studies show that many people show a false sense of self-confidence in attempts to establish and adhere to a deadline. In one of these studies, researchers asked students working on class assignments to indicate time within which they were 50% certain they could finish the project as well as a date when they were 99% positive it would be completed.
The results? Only 45% were successful, showing that even for deadlines they were virutally certain they could easily beat or meet, their degree of confidence far exceeded their actual accomplishments.
The lesson in these studies boils down to this: "know theyself" and set realistic expectations (one of our six tools of anger control) regarding what we can accomplish in the future. This should be based on a realistic assessment of our abilities, our past accomplishments, and a realistic assessment of possible obstacles that need to be dealt with to accomplish our goals.