Imagine a person living alone on a prairie. He tries to build a house, but he is too weak. If he manages to build a teepee out of leaves and sticks, it soon falls down in the wind. He tries to hunt an animal, but he has no way to trap it, and it escapes him easily. We need other people to survive, and the more other people we have, the better off we are. If you doubt it, compare New York City to any jungle village. It is true that there is power in numbers.
Now, people have predictable reactions to certain stimuli. Perhaps the most primitive example is tickling, which predictably elicits laughter. On a higher level, telling a joke often gets a laugh. Personality traits can also function as stimuli of this sort, even if they are not being used: a tactful person is likely to get more favorable responses, even if they are not doing anything overtly tactful. Some people have the skill of eliciting favorable responses, either innately or through practice, either by the means I've just described or through others. We say these people have social skills.
Because man is a social animal, having social skills is beneficial in every area of life. If you have social skills, you can organize other people toward your ends. This means a better job, more money, more knowledge, etc. In short, social skills provide the person who has them with all the advantages of New York City over a jungle village.
The lesson is, if you want to flourish, think about what stimuli tend to produce favorable responses in people, and try to create those stimuli in yourself. Otherwise, you'll be like the man on the prairie, alone and helpless in the face of the elements.