Before you can successfully sell and market a product you have to be intimately familiar with its features, strengths, benefits and weaknesses. Selling and marketing yourself is no different.
Knowing yourself covers many aspects and the reason you need to know yourself is because of the necessity to interact with others. The better you know yourself the better you can adjust your approach if necessary at interview.
One way of considering yourself in relation to others is to se your personality as a series of windows, with each window representing a different aspect of your personality as seen by yourself and as seen by others. This is Joharis Window.

The Transparent Area
Things known to you AND known to others. There is free communication between you and others about these aspects of yourself.
The Blind Area
Things known to others but unknown to you. Others perceive these aspects in you but you are unaware of them yourself. These aspects can include both strengths and weaknesses you don't realise you have.
You project who you are through your persona and you may not always be aware of the effect that your less conscious behaviours can have on others.
Examples of potential "Blind-spots" could be:-
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Telling rather than asking
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Impatience and therefore insensitivity to the feelings of co-workers
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Failing to seek or accept common-sense advice
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Operating on a "short-fuse" that may lead to being considered loud, aggressive or domineering
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Seeing things only in "black and white" and therefore failing to see the "grey" areas in life and work. This potentially leads to being less adaptable.
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Dislike for predictable routine
The Hidden Area
Things known to you but which you choose, for whatever reason, to hide from others. These may include your feelings about others that you keep to yourself.
The Potential Discovery Area
Things unknown to yourself AND unknown to others. Both you and others may be unaware of, or perhaps vague, about many aspects of your personality. It may just be an unusual set of circumstances that reveals a different aspect you didn't know you had and which others hadn't perceived in you before.
Clearly what you are attempting to do is increase the size of the transparent area by pushing out the restrictions imposed on your true personality by the Blind and Hidden areas. By doing this you move into the Potential Discovery area as represented by the small green box.
Discovering your true potential takes self-awareness, intelligent listening and a positive attitude to what you may perceive as criticism. It also involves working with friends and colleagues to find out how they feel about you - what things come across strongly to them? What weaknesses, what strengths do they see?
This has been a very simple look at Joharis Window. If you have found it interesting the web has in-depth articles and advice on the window and how to use it.
The point is...
You must be comfortable with yourself when you go for interview. And the better you know yourself the better you can sell yourself. However, the challenge, if there is one, is to accept the fact that dealing with unknown aspects of your personality requires an openness that may not come natirally. Try experimenting, you might just find out something that will pleasantly surprise you!