I think many of these “don’ts” fall into the category of “Don’t be too relaxed or too open.” Job interviews are stressful. Your interviewer is most likely a well meaning, kind individual, who wants to put you at ease, and wants to like you. That’s great, and if it helps you to relax and make your best impression, the interview will be that much better for both of you. But, don’t mistake an interview for what it is not. This is not a friendly chat, and it certainly isn’t a therapy session. Just because someone is open and cordial does not mean the interview rules have changed.
I remember many interview candidates sharing way too much. I’d ask why they were looking for a new position and I’d get an endless list of the things their boss did wrong and the company did wrong. Remember, the person interviewing you does not know you. Your future employer wants a capable individual who will be easy to work with. They have no way of knowing if your crazy boss is really crazy, or if the problem was with you. Don’t give your future employer any reason to question your ability to be a team player.
I also remember desperate job candidates. They’d tell me things like how hard they were working to find a job and how little success they were having. A comment like that would make me question why no one else wanted to hire this candidate. Are you more likely to walk into the deserted restaurant or the busy one? The busy one, of course! If you tell your interviewer that no one wants to hire you, you look like the empty restaurant.
Another way interview candidates shared too much was in telling me that they weren’t that interested in the job. Things like, they’d take the job as an emergency measure, but they really were looking for a job two levels up. Hiring and training a new employee is expensive and a lot of work. Nobody wants to go through that just to have the new hire be unhappy. If you can’t be enthusiastic, fake it, and if you can’t fake it, don’t bother interviewing.
If you’re looking for a new job, you’re probably feeling a great deal of stress, and that’s OK. Just share that stress with an appropriate person, like your friend, or a family member, or your therapist. Not your interviewer.