In some ways they have similarities with social dates, first dates. You can feel a bit nervous, might feel intimidated; did you say the right things, did you handle yourself well. Everyone says, be yourself. It's the same for job interviews, be yourself. Be prepared, show interest, don't be overconfident, etc.
And like first dates, you can do all the right things, etc. And you think things went well, but, you find out that there is no second date.
"Be yourself" is a very weird piece of advice, and very often the wrong thing to do.
Do you want an offer? Don't be yourself: be who they need. If it requires you to be a bit different from who you are, so be it.
Once you get the offer, the power structure changes: you're the one in control. You're the one now faced with the tyranny of choice. This is when you can decide whether accepting this job would be at odds with who you are. But you know what? Even if that's the impression you got from the interview, your job at that company might still end up being different. You could end up in a team that's completely different from the ones who interviewed you. Or the job might end up being different. Or you might end up finding out you like things you didn't think you would.
Get an offer. At all costs. Then you're in charge.
My point is when you're interviewing, do your thing, show them what you have, show them your capabilities, your dedication, vision, whatever, using your way --using 'zak_mc_krackens'' style is not going to work for me, because I will not wear it well. I won't do your technique justice. Sure, over time, one learns how to refine interviewing skills/technique, but we do it in our own 'voices'.
Don't over think it. As I said, you can do everything just right, but for whatever reason, they pick someone else. They may even consciously come to regret their decision --just like in dating. Interviewing and dating are more art than science. Sure, be prepared, show your stuff, but none of that guarantees landing the job. So there is no reason to beat yourself up for not getting the job.
It depends on how you want to interpret "yourself". Our selves have very many facets. We have the at-home facet, the with-friends, the one at-work, the one in front of a court. They are all our self. It basically means be natural for the face you're putting on. Don't over do it. Don't construct something overly elaborate such that it misrepresents you and it becomes apparent. Don't over think it.
I don't have a "write some algorithm in 15 minutes" self because I never do it at my job, but here I am, trying to rush an implementation on a whiteboard.
Part of that is doing research and getting to know what the company looks for in candidates and what you can expect in interviews and how you meet them. Sometimes it won't be a good fit, and that's alright.
If they want you to be their monkey and that's not you, I'd say don't do it. Of course, that's very easy for me to say, but if you think it's unreasonable and don't like it, find another company. There is no "one" company --just like there is no "one" romantic partner. It's all about trade-offs.
And like first dates, you can do all the right things, etc. And you think things went well, but, you find out that there is no second date.