You Must Understand The Psychology Of Other
This allows you to relate and understand people on a much better level. You will see where they are coming from, what influences, motivates and shapes their lives how they see things and the rest. Without this understanding, you cannot relate to people and fully understand where they are coming from: you will not fully understand their words and actions. The only way to understand someone's words and actions on the most fundamental, true and complete way is to understand the psychology of people.
You Must Understand The Signals That People Provide You, And Interpret Them Correctly
Non-verbal communication is the highest level of genuine communication, because it can't be easily faked. We can easily fake our communication with words, but our body language almost always tells the true story. By understanding what someone is truly saying, you will be able to act accordingly. If you miss what they're saying, you may miss an opportunity or an understanding of that person. This is particularly true in job interviews, corporate environments (e.g. board meetings, reviews, client pitches) etc etc, throughout your personal life and relationships with friends, family, colleagues etc. Learning how to understand people is fundamental to success. It allows you to go through life easily and with little friction. By missing the signals of people, frustration and lack of understanding can easily result leading to friction.
You Must Understand That People Are Weak
People are not perfect, and everybody is trying to do their best, giving the level of understanding they have. You will always have to accept people the way they are, including all their weaknesses. You may need to practise compassion and forgiveness on a regular basis to see you through.
You Must Always Be More Socially Intelligent Than Other People
Being more socially intelligent allows you to be ahead of everyone else, and see the situation for what it really is. Every now and again, you should sit down and analyse your social relationships with other people. You should see who is a liability in your life, who should be actively kept in touch with, who is drifting away from you etc etc. Knowing your social relationships and how everything is working between people will allow you to stay ahead of the game and make the best decisions.