The Ebb & Flow Of Friendship

What are the common elements in longstanding friendships you have?

Aside from an obvious element like trust, I've been having some difficulty nailing this down. It often seems to me that the ebb & flow of my friendships is a little fickle. For example, an element as superficial as proximity sometimes seems to play an outsize role for me. Given how easy technology has made communication, I've begun to wonder if those geographically proximate friendships of mine were ever friendships at all. And seeing how my wife has maintained a powerful friendship (with and without technology) with a high school friend who has lived in Florida for 40 years, I wonder more about how real my friendships have been.

Lately I've also noticed I'm less inclined to hold onto a friendship that begins to have any whiff of competition. What has been your experience with this?  Like many of you, I've seen those "friends for a reason, friends for a season" explanations about this ebb & flow. At times, I get solace from those Hallmark sentiments. Today, not so much. Today, I'm interested instead to know what you've learned.