Another factor is how good your interviewer is. Some are well trained, extremely friendly, and do a great job of making you feel comfortable and at ease. They realized that interviews are stressful and so they try their best to make the experience less daunting. Others are untrained, inexperienced, distracted or unengaged. Maybe they even give off strange body language or make weird eye contact — simply put, they are not very good at putting you in a comfortable state so that you can do your best. Obviously this can have an impact on your performance. Obviously, this is not your fault.