You are the average of the five people whom you spend the most time with. – Jim Rohn
In terms of human performance and self improvement, it is often the things which are consumed that influence the culmination of who someone becomes. This is a result of how information affects the mind; that which is consumed is used as a reference in all future cues and encounters, acting as the filter for experience, belief and action.
It makes sense therefore to assume that the individuals which have their time spent on make up a large part of who someone becomes; the actions, words, behaviours, beliefs, emotions, attitudes, perceptions and opinions of others are all pieces of environmental content that are consumed.
From here a conclusion is made, that a person becomes the average of those they spend their time with.
To become the very best person that one can become, it makes sense that they would invest their attention and time into the very best people that they encounter. To reduce poor performance, beliefs, behaviours, thoughts and more, it makes sense to remove individuals who bestow negativity upon an individual.
It is thus recommended that we choose wisely who we invest in our time in. Those who support, believe, are truthful, invest time, are proactive, and want the best for you are a great starting point.