The fact of the matter is people sometimes think they have outgrown a friendship. If I reach out to someone about why they have decided to opt out of a friendship and receive no response, I feel no sense of loss whatsoever. Even if that person thinks the matter is insurmountable, unwillingness to engage in discussion implies there is some moral or ethical or selfishness issue implied in the decision to dissociate.
If we are talking about a romantic relationship, clearly this is a different matter. A guy can treat a girl right or vice versa by refusing to explain why he or she no longer desires to be in a relationship whenever that decision is a firm decision. This prevents wastage of the other person’s time in event they would respond with an “I can address that attitude.” The right attitude implies of course the discussion centers around an “I have concluded this will not work for me and as such need to release both you and I from this commitment” kind of talk.
With friendship, however, we can discuss then choose to remain friends or walk away from each other with full knowledge of the wedge that has generated the falling out. In this scenario, there does not exist any reasonable rationale for a lack of response other than some ethical, selfish, or moral wedge. In such an event, I conclude that person was my friend because they were benefiting something from the relationship, something they think they now no longer are in need of; or they have chosen to align with a group that does not simultaneously desire to align with me. But you see with the alignment thing, I would not begrudge that friend his or her decision, which they feel is best for them, because at least I understand better who is not aligning with me — a passing gift from the friendship that now is ending.
The beauty of it all, sometimes those who walk away from us without explanation, thinking we no longer are of any relevance to them, find out later they were more wrong than right in that decision.
One of my life principles is never to allow rejection change how I see myself. So long as we can be honest with ourselves about who we are, where we are coming from, where we are at present, and where we aim to be, indifference to rejection not accompanied by explanation is safe, healthy, life enhancing, and a stepping stone to self actualization, progress, and stability in our lives.