To a large extent we are shaped by our environment. Specifically people. In our early lives its our parents. Much more than character, and opinions are influenced. Parents also encourage or discourage certain behavior or inclinations that we have according to what they feel is right as well. Often people find on hind sight that even our career choices have been influenced to a large extent by our parents, either by encouraging us to study along a certain field that they like or feel is suitable for us, or by our own actions of rebellion against these encouragements. Encouragement/discouragement also enters into the child's development through other elders and teachers whose opinions we are taught to value.
As we grow older, these authority figures become less of an influence as we tend to form our own opinions and not take what is told as face value. But our opinions are still not entirely our own. It is still linked to the people we hang around. Living away from your parents mean you grow closer ties with friends as a support system and their opinions begin to matter. Having conversations with friends and colleagues lead you to broaden your perspective and you tend to assimilate some of the general opinions. Those who are more stubborn or strong willed tend to hold on to their preformed notions while those more weaker willed will tend to sway with a group opinion.
These are common people who influence everyone. But take a specific example of grad students and you find that a lot of them are influenced by their supervisors. More than in a common work environment where there is a chain of control, and people come and go, get promoted, work in different groups and so on; a grad student has a close relationship with their primary supervisor for 4 - 5 years in general and as this is generally their starting point of their professional life a lot of cues are picked up from the supervisor. From very basic things like presentation/writing styles to more character issues like how forceful, perfection oriented, organized etc. In some cases where there is a chance to evaluate and choose supervisors/students its likely that people of similar character choose to work together, however even when thrown together randomly, by the time of graduation a lot of the supervisors characteristics are mirrored in the students. I cannot say if my initial assumption that this is not so common in workplaces is true or not though.
