What is "cool"?
Answer: Cool is a self-assigned feeling of superiority, based on belonging to a group of people, or having superior dress and superior objects.
Why is "cool" cool?
Answer: We evolved thus. There are certain definite advantages with cool. In stone age days, belonging to a group improves one's chances of survival. Superior dress, i.e. warm clothes, also improve one's survival chances. Same for objects such as weapons, shelter, cooking utensils, and so on. Thus, people with the character trait of "cool" survived and thrived in greater numbers than people without the trait.
Is "cool" relevant today?
Answer: No, maybe not. It has little affect on one's chances of survival in the modern world. However, there is one aspect of cool that might be relevant. Beauty is cool, to be attractive is part of the trait of cool. And being beautiful is very important for relationships, mating and reproduction.
Now that I know what it is, the question remains if it is desirable and obtainable. There are certain benefits and advantages of being cool. Cool people seem to have more fun, are outgoing and easy going. Cool people connect with each other better, and help each other, while the not-so-cool are on their own. Better jobs through connections. Attracting and keeping other cool and beautiful people as friends and lovers. Making more money, buying better homes and other things.
In order to achieve coolness, cool people have an unconscious sense of cool. They have this sense, and apply unconscious and final judgment on other people and objects. People and things judged to be cool or have coolness are desirable. Other people or things are shunned. This judgment process is continuous. To be cool is to be judgmental critical, disapproving and disparaging, implying a negative impression. Cool people think of themselves as discerning, discriminating, sharp, astute, perceptive, sensitive and shrewd, all positive attributes.
Conclusion: Cool - get it if you can.