Common Mistake #8: talk too much at an interview
While most quant candidates tend to be the quiet type, it’s not uncommon at all to find some who, for one reason or another, tend to talk a lot during an interview. They talk so much that they leave the very bad impression of trying to dominate the interview, which makes the interviewer upset as well as suspicious of the candidate’s motivations: is he/she trying to avoid answering any technical questions?
As a candidate, your role in the interview is to provide answers to the interviewer about your quantitative aptitude and your personality. You have every right to explain yourself and to do your part to find out what the job and the group are like, but, at the end of the day, you must impress the interviewer as both capable and agreeable.
As my book bluntly points out, in the interview hierarchy, the candidate is necessarily in an "inferior" position relative to the interviewer, and, his or her concept of social order notwithstanding, it’ll do well if he or she observes this hierarchy. Also, it pays to look at the situation from the interviewer’s POV: if you were the interviewer, would it give you pleasure to talk to someone who constantly interrupts you and peppers every answer with an endless parade of BS?
If you are a sociable type, play that to your strength at the interview by saying the right things at the right amount. Remember: nobody likes a chatterbox, even people who are chatterboxes themselves.