"Just be yourself" and "Just be confident" while well meaning aren't the greatest advice in many cases. Alternatives are "Know yourself, your strengths, your weaknesses and seek self improvement," "Be honest with yourself about what you want and what you are willing to do to get it," "Set realistic achievable goals and set new ones when you achieve the ones previously set."
The first allows you to accept reality and realize that you can change for the better. The next makes you come out and say to yourself what it is YOU really want. Not what someone else said you needed or should want and not out of envy for what someone else has. The last is a simple yet potent method of building confidence. You have to start somewhere. You can't just "Be a champion" or "Be the best" because you said so.
Not directed at anyone who said "Just be yourself" or "Just be confident." I'm not wanting to put anyone down. This is just my perspective on how to expand on these bits of advice I used to receive but never understood until I failed enough to find better answers to the questions I was asking.
Yes, of course you should be yourself, as there's no one else you can be. It is also good to be confident. What often is missing from these well intended words is what we really mean when we are saying them. It's the what, but the how is missing. Sadly, many people just do not know how. The student isn't always going to be saying "I don't get it!" or "What do you mean?!" or admitting their frustrations when they later try to justify their failures. Ie... "I was being myself just like you said and I *always* get turned down." or "I try to be confident and I still never succeed."