As I see it, you can make friends in only two ways: one is a emotional journey where all your personal firewalls break down and you almost know how the other person feels like. Another way is through gradually increasing appreciation for someone where at a point you actually know what your friend is thinking. Now hold a moment before saying that friendship can’t be this much black and white. It’s usually not and I am not claiming otherwise. Ideally you can call a relationship a friendship when these two sort of connections work together in a complementary way.
Most people don’t give that much thought about this because either your connections with someone is complementary with each other and you are friends with them, or not complementary at all hence you just don’t “click.” With time your friendship grows and the contribution of one of these two aspects rises and other falls. If you observe carefully, you will see that you don’t talk with your childhood friend now the same way you used to talk when you were a child. This is because the most of the emotional pull has converted in to rational understanding over time. It’s not like you don’t feel love for your friend, it’s still there but you now think of them in terms of cause and effect. Sometimes this change is perceived as being more “mature” whereas it’s only you being more logical towards your companionship. Same goes for vice versa when you see people defending their friends even though they did something really bad.
Sadness is, when you realize that your emotions and rationality don’t complement each other in your relationships. That’s when you start losing ties with your friend. Mostly it goes unnoticed, but the process is painful anyway.