Let’s say you and some people you know decide to play soccer together. Sounds good! So you get going and you start playing and you end up with a really good game going: it’s been going on for like, 151 years, or 241 years, something like that. Sure, there were times when fights broke out between the players, but in general, the game is successful.
The goal of the soccer game is two fold: (1) is you want to have fun with people on your team and people on the opposing team, and (2) play in such a way that they will want to continue playing with you forever. When you always loose, or play dirty, or any number of things, both (1) and (2) are at risk.
Who should you then not play with? How about “people who don’t play by the rules.” You shouldn’t play with people from the other part of the neighbourhood who only play tackle football and will use the rules of tackle football when playing soccer. That’s no fun because the game ends violently.
Who should you play with? Or rather, who should you bring into your team? Well, selfishly, you should bring in people that will support your team. Players from the other side of the neighbourhood who were extreme ballet dancers for the last 9 years and so don’t have an underdeveloped muscle anywhere on their body. They would be useful. But if you do this, then the other team will also do it to, so in the end, both teams end up getting better.
You should be discriminatory with your preferences for people who you’d like to join your team, or else bad things happen.