Proverbs 27:17 - As iron sharpens iron, so one man sharpens another.
People are born social in nature. Studies show that people who engage themselves more in social activities tend to be more happy and free from sickness due to a more highly immune system. Some attribute longevity to the social support system one can get by belonging to a group or to someone special. With the advance in technology and with the availability of social networking sites, it is easier for any human to interact with other people even inside the comfort of their home. So being alone now is not an excuse, no matter who we are, how we are and where we are.
The bible knows the importance of human interactions; it can both have interpersonal benefits as well as psychological benefits. Each person's customized experience in life can be used to sharpen the person whom he/she interacts with. Iron in the bible symbolizes strength. So one person can be the source of encouragement of another person if one feels weak in reality.
I remember, when I was still in college, we discussed in psychiatric nursing that each person has his blind spots. These blind spots are the things which are unknown to the person but known to others. So we need each other for correction to point out to us the things that we need to improve. And I can say I personally become more mature in faith by fellowshiping with others.
Somehow we need not to use this psychology thing to improve a person. God knows how to orchestrate things to sharpen one iron by using another iron and thus the two irons benefit from the sharpening, in the end.
I was once praying with a friend. And I noticed that this friend of mine can pray longer than people usually can. And we can both have our prayer done in 30 minutes or more. I jokingly told him that he prays longer than my pastor does. And to my surprise he told me that I influenced him somehow to pray longer like that. And I remember in the past, just before having been acquainted with my friend, I did not know how to pray long. Therefore, unknowingly he is doing things because I influenced him, only to find out that it was him who really influenced me to pray the way I pray now! Remember, I did not know how to pray, before