Many of us have often heard others say we should "be more confident", "believe in yourself", etc. You can all make your own list of examples.
There seems to be evidence that confidence by itself sometimes breeds success. When I say "confidence by itself" I mean believing in your aptitude, personality, etc regardless of whether or not you actually have those things. So believe in your skill even if you have none or have it inadequately. Be confident, show that confidence to others, and you will succeed.
I read a psychological science paper by Norem and Chang (2002) which suggested this and gave that strategy a name: "strategic optimism". It involves not only avoiding negative thoughts (which the "be confident" crowd would champion) but it speaks well of actually having positive illusions (Norem & Chang, 2002; Taylor & Brown, 1988).
However, Norem and Chang also talk about the other half of the story, one which echos the sentiments of many of us who are frustrated with the "be-confident" crowd: sometimes strategic optimism doesn't lead to success. Sometimes it's better to imagine the worst, to have low, low expectations ("unrealistically low"). This strategy is called defensive pessimism.
The paper says that the research suggests that strategic optimism and defensive pessimism work equally well for succeeding at tasks. And that a person will perform better if allowed to use their preferred strategy, whichever it is. This adds some hope for those of us who prefer a "to each her own" strategy. In other words, if "be confident" works for you, great. But don't assume it will work for me. Not only are you possibly imposing upon me (violation of my and many others' libertarian views) but you are doing the opposite of what you are intending to do: promote my success.
The true and good intentions of a "be confident" preacher should be recognized until he or she proves otherwise. But by now we know good intentions don't equal good effects.
On the other hand, there are those that can't stop criticizing. "Pedantic" is often a fancy name for them. Ironically, it's these often these same people who end their sermon do's and don'ts with the "be confident" preaching. Essentially we are told two messages: "you can be do anything and should believe that" and "you can only do this, this, but not that, but only this is this way...."
These people are not necessarilly overly-critical. A lot of them, I think, are telling exactly what is true and nothing more. I wouldn't call them "pedantic". But sometimes it may feel that way on the receiving end. There may not be anything that the advisor can do because they are already staying within the lines of being appropriately-but-not-excessively critical. This is probably where the phrase "suck it up" comes into play, though I personally feel that is an ugly phrase to be said against another person. But I have few qualms about saying it to myself, and I suppose others feel the same, meaning a lot of success-motivated people are telling themselves to "suck it up".
And this may be where the un-optimistic, hyper-serious facial expressions (or lack of expression) emerges for any person being coached, mentored, or otherwise given advice. We look anything but confident and excited, and yet we are told (if not by the advisor, then by the rest of the world) that we need to show confidence and excitement on our faces. I'm sure there is psychological evidence and definitely lots of anecdotal evidence that shows that smiles and confidence get you the job easier than those without. It makes sense to think these things, separate from real skill, are necessary. And yet, they are kind of dependent on real skill, because if you don't have the skill, or have not prepared sufficiently, how can you feel confident? What reason do you have to be? Don't forget, we are also advised by the world not to be overconfident, "pride cometh before a fall", and a hundred thousand stories of people who thought they were all that only to have reality "slap them in the face". And the lesson? They needed that.
Why not avoid such folly by assuming less than confidence would have you believe?
Every adult has every reason to be confident they can add single digits, that they can walk better than an infant, and that they can control their hand to turn a doorknob. Beyond these low-grade examples, there are hundred other things we can and should be 100% confident in. But these are things that are true beyond a doubt. Judgments of whether I know enough to answer this or that interview question in the right way, with the right emotional expression, excluding these or those words, all of which may change from interviewer to interviewer....to assess if one is ready for this is a far more ambiguous assessment. There is always room for realistic doubt (or nearly always, see told you). The success-obtaining value of showing confidence and smiles is real. But you also want there to be answers behind that confident grin.
Finally, I think there is another value besides success. There is also the value of being your own human self in whatever human emotional state you are in. And I'd like to think others ought to be tolerant of others emotional states, unless they involve an angry attack on them. While the darker, more serious moments on our faces are sometimes considered less "human" than the ideal of a laughing, confident, life-is-too-short demeanor, really all of our emotional states are human because we do not change species when we shift emotions. I turned to psychological science in this blog post because the field has in many ways a greater appreciation of the diversity of human expression beyond what society considers ideal or "normal". It was society that considered being gay "a sickness" and it was scientific psychology that disproved that, after cleaning out its own biases. I can't say nerds in the psych department always know more than people living in the real world. But we do have access to some objective thought strategies that can shed some light on so many claims made by people: "be confident", "suck it up", etc.
I know this means that sometimes the people making those claims will be proven right (at least until more evidence comes in). Though that is probably why I chose to end this piece talking about the value of freely-felt emotional states. Because even if psych science shows that the preachers pushing me to act and feel against my desire are truly bringing me towards a successful interview or whatever, will it be justified? Don't forget, we have "ends don't justify the means" principle. Though I know we choose to break it a lot and that is what defines much of mature pragmatism. And I can support a lot of that.
I think that it is always good to learn as much as we can about a place before we have an interview there. Learning about the place means learning about the culture and the people there. The advantage is that you can hopefully see how much of your true insecurities is ok to express. In social psychology, they call these "display rules", and we already know such unspoken rules differ between cultures.
A place that does work with weird results (like scientific research) might have folks in the place of employment that are all-too-empathetic with colleagues that looked frazzled. In some places, it is more ok to let them see you sweat (or have an unsmiling/nervous face).
It's searching for places you fit.
Norem,J.K. & Chang,E.C. (2002). The positive psychology of negative thinking. Journal of Clinical Psychology, 58 (9), 993-1001
Taylor, S.E. & Brown, J.D. (1988). Illusion and well-being: A social psychological perspective on mental health. Psychological bulletin, 103, 193-210.