This article originally appeared in Well+Good.

Friendships are a living breathing thing—just like the people who are in them. That's to say, they can change over time as a result of any number of factors: life events (moving to a new place, changing jobs, and getting married); shifts in the ways in which we tend to interact (like the growing influence of technology on relationships); and the simple passage of time.

Any of these conditions can boost your connection to a certain friend or diminish your closeness to another. But even as relationship dynamics ebb and flow, the key elements of any friendship, whether close or distant, should always remain intact.

Broadly speaking, the core qualities of good friendship hinge on a simple tenant of any relationship: being present. Or, as friendship researcher and coach Madison Romney puts it, being “psychologically available” to the other person.