Human were not created with the intention of living life alone. Even the creator of everything realized that humans need companionships in order to be balanced and happy. Therefore living alone or opting to lead a life with little or no contact with other is indeed sad and may even lead to mental and physical problems.
Sometimes it requires a focus and mental effort to form relationships with other people. For some this can be a rather difficult and embarrassing experience as they are really not comfortable or not confident enough in their own selves. Furthermore it can be quite difficult and challenging to actually set aside time from an overwhelmingly stressful work life to then have to deal with the stress of forming new relationships. Here in lies the initial problem as most of these people often look upon the exercise of forming new relationships as stressful. It would be wise to address this particular train of thought as it does play a very important and sometimes destructive role blocking the quest to start new friendships.
Once the confidence levels are present then the initial apprehension faced by the person will lessen to a certain degree which allows for the more adventurous mind set to prevail. The confidence gained is then apparent in the individual and this then becomes a very attractive quality which in turn attracts others to the said individual.
Making the effort to be part of something is also another way to ensure the individual does not lead a lonely and reclusive life. By being part of an organization, team, social group or even part of a games team will definitely create circumstance where there are opportunities to socialize and make new friends often. This then can also snowball into a very active social calendar.