A human life is divided into two paths - The path of social interaction and the path of self-reflection.
The path of Social interaction leads one into contact with other people and allows one to function within the broader society that surrounds us. The path of self-reflection leads one away from society, allowing one to spend time alone, introspecting and reflecting upon one's personality, and developing accordingly.
One must walk with one foot on two paths for if you choose to walk fully in one you will end up lonely of purposeless.
If one walks fully and solely down the path of social interaction then one’s existence will be defined by how one is perceived by others. Although this path can provide entertainment and company, it also leads to a purposeless existence as one derives purpose from the acceptance of others and not oneself. If you look at a person that finds all their fulfilment through their acceptance by the society around them, you will notice how they require company and often live a life without purpose.
Conversely the path of self-reflection leads one to discover their true being and to develop accordingly. This provides one with purpose to existence, however, this path also leads one away from society and the path of social interaction. If one continues solely and fully down this path one will eventually be cast out of society. You will often see people that have spent too much time alone and introspectively seeking purpose at the expense of social interaction - They are often unable to function in society and forgotten. Being cast out by society and is cold and lonely as we are social beings... Society us like an open fire – it warms you from the cold.
To be happy one must function within society and also have a purpose to one'e life. To live a purposeful existence one must spend time alone, reflecting on their purpose. To live a social life one must be a social being, interacting with others around them. Walking fully in either path will lead to unhappiness as both a purposeful existence and social acceptance are necessary for happiness - The happy person will walk with one foot in both paths - living socially and with purpose.