So it was an evolutionary anthropologist, Professor Robin Dunbar from Oxford University, that had said that this number is 150 (also known as "Dunbar's number") is based on his research into the number of trusted relationships we can maintain throughout our life. This is our 'cognitive limit' (mental limit), which makes sense as it reminds me of one of my favourite quotes where we can't always do everything, but we can always do something. As our friendships generally weaken when we may not have been in interacted with the one another for a while, and we can only really interact well up to a certain extent. He further points out that often these are people are generally physically close to us to give us that sense of community, which makes sense as it's easier to stay in touch more intimately with those closer to you.
In a time of globalisation and greater connections, I wonder what that number would be like for each of us, whether it is indeed the 150 (actually 148 but rounded up) that Dunbar number refers to, but that debate can go on forever...
Either way, I think the main benefit of his research is that it helps us understand that while we may try to have as little or as many friends as possible, eventually there is only so much close relationships you can have. I'm sure everyone has their own ideals, thoughts and personalities which all play a part in how many people we tend to stay in contact with.
So what I believe we can each do now is ensure that we look at focusing our efforts on creating quality relationships rather than worrying how the quantity (i.e., the number) of relationships we may have. So keep those relationships going with those you'd like to continue to remain in contact with.