Growing up, I was a one friend per year kind of person. I had one specific friend in school, and one specific friend outside of school (only because she attended a different school). I ignored most other people, and tended to ignore my friends except during those specific "school" or "play" times.
I was not a nice child.
In college, I learned about variety in relationships, specifically proximal friendships, meaning you're friends because you're in proximity to each other. Most friendships fall into this category, btw. Close when physically close, and separate when separated. These can be intense relationships, but they rarely outlast a change in distance.
I've made deals with several friends since learning this. We will never recriminate on why we've fallen out of touch. Each meeting will begin with the enthusiasm of a dog greeting an owner, no matter how much time has passed. It works great, as long as you really mean it. Which I do.
When I think the word friendship, though, I think of something more. That C.S. Lewis definition of "What! You, too? I thought that no one but myself..." A similarity that goes beyond working in the same office, or attending the same Sunday School class. A similarity of worldview.
I have tried to expand my friendship base as an adult. To be friendly with those not like myself and enjoy our differences. It is useful to measure life against a different viewpoint, and one of the benefits of a true friend is enough difference in perspective to keep conversation interesting.
However, some perspectives are just too different. I may love, admire, respect a person, but if the differences in our worldviews are too pronounced, they move out of the friendship circle into the proximal friendship circle. This may be a sudden shift or a gradual decline.
I have heard friendship likened to a well (although maybe a money jar is more accurate). A friend must contribute to the well before drawing out. If more is drawn out than put in, the friendship cannot last.
In a perfect world, I could be friends with everyone. I could handle all differences and never find opposing viewpoints toxic. I do not live in a perfect world, and I am far from perfect. I do not find comfort in contention. I will do my best to minister daily to the world around me, but my friends enjoy a special, peaceful, pleasant place in my heart, and I will seek them out for that reason.
Push button. Receive bacon.