I'm writing a novel in which several of my characters interact closely so I've been thinking about character development. There are plenty of lists and software programs that lead writers through creating traits, history, personality type inventories, and even psychological disorders. Here's one. Here's another.
We write dialogue, interior dialogue, and character behavior to give readers information about the character and narrative arcs of our stories. By communicating nuances of interaction, especially where unequal power dynamics exist, we show how our characters affect each other on a psychological, or subconscious, level.
Even minor characters can exert influence.
For example, when an interviewer (like an employer) has prejudged a potential employee—because of something they've been told or because of some inherent prejudice, for example—that belief or expectation is transmitted to the interviewee (usually subconsciously) and can result either in the interviewee becoming more confident and comporting themselves well, or (in the case of a negative judgment) in the interviewee losing confidence and comporting themselves less adroitly than they might otherwise. It can become a self-fulfilling prophecy for both characters.
On the other hand, it can be the catalyst that causes our characters, particularly our point of view character(s), to overcome some interior obstacle and move toward greater freedom, independence, and self-actualization.