Why do competent candidates, sometimes, fail to impress in interviews?

Just like in sports - every candidate has his/ her good and bad days!

The candidate might not be prepared, have a poor self confidence, negative attitude on answering questions, lack of focused. 

In an interview candidate must be well prepared because the interviewer will assessed how accurate the candidate CV is. Common factor considered during an interview is the candidate's personal appearance, manner on how the candidate answer each question or scenario, communications skills, the intelligence and maturity and the sign of potential capacity of growth.  

I think that the more they need the job, the more they fail to express how suitable they are. An interview for a terrific job may be a huge stress on the candidate.  

a few things i know would affect the result of a competent employee at an interview include:

• being over confident and crossing the line of arrogance
• poor preparation as he would rely on what he had learned overt time without revision
• failure to pay attention to details - instead, he is focused on over selling himself

You can not judge the competence just in few hours. It happens due to communication issues sometimes. 

its the interviewer mistake most of time as he is the responsible to ensure the interview environment which encourage that the candidate out all what in his pocket , as i believe that alot of recruiters excellent in sourcing and finding CV but not good in managing interview , and they think that the candidate has to lead the interview

As it's a open ended question and there are many reasons , but i think these are the important one,1. Over Confidence cause bad impression2. Having no proper industry knowledge3. Trying to speak more but not relevant4. Feeling stress & voice pitch changed

Thank you for invitation

I agree with all answer 

Because most of the time they show their weakness during the interviews.

Hello,

I agree with with all participant

Best Regards

Competent candidates fail to impress in the interview because they do not go with an open mind for the interview.  Every interview is differnet and the nature of it changes.   Experience is an important factor and part for an interview but they are always looking for outstanding people.  Why? Shortlisting candidates is important for an interview as this streams down the line of candidates and gives the company a better hand in knowing their candidates.  Candidates have to be jovial and serious (both of these depends on the type of question posed by the interviewer(s).

This is so much the case in a world filled with so many applications for one job examples in one vacancy there are 10000 applicants out of which outsourced are 500 and 500 are local.  Each candidate in this criteria come with the same experience hence an interviewer or a panel of 3 would be looking at a person who can be a source of inspiration to the rest or a model in the organisation and help the others too.  All the same the person comes with an expectation and the company also expects from the person the same level of participation. 

These come through an outcome in any of the following:  role-play, activities, name game, music and passing the parcel, musical chairs, for and against question to see where you can discuss and achieve an equal target.

When there is nothing to match the person on the level of competitiveness and detail.  These points disappear leaving the person bare of any points (usually interviewers have a very keen eye on candidates when participating in any activity).

The person must be interactive and positive, keep a keen focus on the interviewers and their expectatins, follow the rules and abide by them, make a positive mark to achieve their grade in an interview.  A selection is not easy but can be achieved when the level is met.