There is a great characteristic that a friend should have and that is perfection. This perfection is not in the standard way we think about perfection, though, it means instead that it is perfection that talks more about understanding that each friend has their own faults and that each accepts those faults of the other. 

"Every man should have a fair-sized cemetery in which to bury the faults of his friends." ~ Henry Adams

No one is a perfect human being. To me, it is impossible to be perfect. This does not mean, however, that imperfections should stand in the way of being good friends with another. 

One of the keys to establishing a friendship in the first instance is to have common ground upon which each other can relate. Such was the case of an old friend of mine when we first met and where our interest in music was the binding commonality. And, this friendship blossomed over the years with greater understanding, more interest, and the ability of each to grow as mature individuals. 

On the other hand, you will meet people throughout the years that desire to be your friend but there are major issues that prevent you from feeling comfortable with this person. Despite their desire to be friends, you are unable to find either common ground or aspects that are totally foreign to your way of thinking and behaving. 

A couple of years ago, I was in that very situation where my friendship was sought but where I could not find any reason to establish a friendship. This particular person had a set of personal ethics that clashed totally with how I though, acted and believed. Is this case, there was no common ground at all. 

Not every person you meet will be a friend, and not every person will want to be friends with you. What is important to remember, though, is that what one sees as common ground is common to someone else and it is only a matter of finding that person to share your friendship with. 

One of the other factors that can derail a friendship is time. In this instance, time goes by and each one of us is usually developing along with it. In some situations, though, what started out as common ground changes and these changes may be of so great a significance that they serve to distance one friend from another. 

For example, where one person's negative thinking may have been overlooked previously, it becomes more and more difficult to continue a friendship when the other becomes more and more positive or solution oriented in both their personal and professional life. As we know all too well, negative thinking people only serve to bring you down in life; they drain your energy. 

The decision to keep a friend also means that as you grow and develop, you would also hope that a friend goes along the same path of development. 

The difficulty arises when one or the other friend seems to be stuck in the same way of thinking and living and has not changed. This does not necessarily mean that their way of thinking or doing things is wrong in and of itself but is more that the other friend is in a different space and time.  

These differences can tend to cause a rift where what was once a commonality of doing and thinking the same way are now diametrically opposed to each other. It is these differences then that can place a rift between what were once really good friends.  

Sometimes, though, it is easier to mend a fence than to construct a new one so one must decide if a real friend is one to keep looking instead at the positives that remain and not focusing on the negatives.