Whereas many burn out or simply fizzle, some friendships stand the test of time, the bond between buddies growing deeper with each disagreement, milestone and hilarious memory. The elements that beckon two or more individuals into a friendship tend to be the same across the spectrum -- shared interests and values, a history together and a sense of being equal, according to general internist and practicing Buddhist Alex Lickerman in his "Psychology Today" article "What Makes a True Friend." The characteristics at the heart of friend pairings vary, though, and certain qualities are associated with more fulfilling and longer lasting friendships.

Predicting Triggers

Beyond being able to list general characteristics, such as “kind” or “patient,” you should know how your buddy tends to react when provoked by various irritating, startling, tiring or otherwise troubling stimuli. Lara Kammrath and Charity Friesen, psychological scientists at Wilfrid Laurier University of Ontario, tested their theory that familiarity with another person's so-called “if-then triggers” impacts a relationship more than knowledge of personality traits that describe the person generally. In the study “What It Pays to Know About a Close Other,” published in “Psychological Science,” the scientists concluded that accurately predicting how a friend will behave in response to a spectrum of bothersome behaviors is related to both minimized conflict and maximized feelings of depth in a friendship.

Benevolent Honesty

Telling you to "go for it!" regardless of what "it" is may be the mark of a pleasant enough acquaintance, but it is not the mark of a true friend, according to Lickerman. Rather than telling you what you want to hear to maintain calm in the relationship, a true friend will call out your concerning behaviors -- calling your ex repeatedly, blowing off school work for video game marathons -- out of a genuine investment in your happiness and well-being.

Encouragement to Be Your Best

Out of respect for one another as individuals, and often for the values each holds, friends don't ask friends to sacrifice principles. If you have a self-imposed curfew because you take your academics seriously, a genuine friend will not constantly pressure you to stay out late partying nor make snide remarks about your bookworm behavior. Good friends are good influences. You act as a worthy mate when you encourage your friend to apply to the best colleges or to date someone who treats your friend with respect.

Responding the Right Way

It is commonly held that friendship only flourishes among those willing and able to listen to one another; however, it takes a specific style of listening and responding to a buddy's emotional disclosures, says Karen Karbo in the "Psychology Today" article "Friendship: The Laws of Attraction." Those friends who really stick seem to have a knack for responding appropriately to big news -- or simply big emotion. Whether or not you consciously assess it at the time, you will most likely be drawn closer to the friend who listens attentively, offers non-intrusive phrases of sympathy and can accurately gauge when it's time for a pat on the back versus when it's time for words of tough love.

Confidantes Keep Confidences

Many would rattle off "trust" as a foremost value in a friend, but perhaps without grasping the full importance of knowing your comrade will not betray you. Julie Fitness, a psychology professor at Macquarie University, contends in the book "Interpersonal Rejections" that betrayal among close friends registers psychologically as a profound rejection that can even cause the betrayed to feel unsafe. Proving, interaction by interaction, that you will not broadcast your friend's secrets or undercut your friend in any way will help the two of you cement a bond that will still be holding strong years into the future.