The Bookstore Says All
Our brain power is limited, therefore it is only natural for us to want to limit the usage of our finite brainpower. And before I get any deeper into this, think of it as walking into a bookstore. In order to find the information that we need, we need to place the data in front of us into neat categories. From non fiction, read the front matter before finally getting what we are going after. So in that respect, we do judge a book by its cover.
Same applies to people, too many to keep track of, so we categorize them. Age, gender, profession, socio economic background and can make reasonable assumptions about them that has a high degree of accuracy. Additionally, some of us have a reasonable idea of where we want to go and what we enjoy. So if a group of people have proved themselves in the past to be of detriment to both your goals and hobbies, why associate with them?
Best to Go With the Rule, Not the Exception
Sure there may be the oddball that defies the odds, but one must ask himself how much he is willing to commit given the slim odds of success. This is of course not an exact science and one cannot boil people down to numbers but it is worth considering. Chances are, there are certain groups of people that are best not to hang around. Characters in dark alleys for one, wielding weapons, most people anyways. Now one can expand that to every category of people.
Because ultimately, life, again is a series of choices, either we make ourselves or others ultimately make for us. As we make more and more choices as time passes, options narrow. Doors close. One of these choices is those we associate with. We have quite a number of daily interactions, but intimate relationships, far fewer. So choose wisely.