I think just about all of us can pretty quickly recall some of our worst times in our lives. For me, one of those times was the damage done to my wife when the small Evangelical congregation we belonged revoked my membership due to my failure to align with the belief that, among other things, the earth is only 6,000 year old and any seeming proof otherwise is just God trying to trick us. My wife, who was recuperating from cancer surgery, was devastated by the rejection but even more so by the sudden loss of so-called friends there. It would be the last time we ever had contact with most of them. The friendships that we thought were pretty deep ended up being very shallow!
I think experiences like this are somewhat common to most of us and as the quote above says they show us the true colors of everyone. Other similar but less stressful events were when we were forced to move to the east coast in order to fill out my pension. We left friends who then just drifted away. Retiring is another example. We for the most part forever leave friends who we have known for sometimes decades.
At least for me, it keeps me anchored to the fact that we are pretty much on our own in this world. Friendships, which are mostly pretty shallow, come and go as circumstances happen. That is just a fact of life it seems.