Proponents of faking it until you make it practically swear by this particular life hack, and to help with an easy explanation, to fake it till you make it means to pretend to be something that you are not to get something that you want.
The simple key or the underlying principle to fake it till you make it is to project a calm and a confidence that a person would normally only equate to someone that is telling the absolute truth; so you confidently present yourself as something or confidently purport to know something, to help yourself along the way to getting that thing.
In an exaggerated example; although I have probably written only two articles in my entire life, I could describe myself to a potential employer as a ‘well versed and seasoned writer, capable of painting the most vivid pictures and putting words to every action’. An interview would see me expounding on literary principles that I had probably just learnt the night before when I had stayed awake poring over Wikipedia pages. As such, my answers would probably not stand up to much scrutiny from the interviewer. I would however state them boldly and confidently and if the heavens decide to smile down on me, I would get the job and make truth out of my claim to be a writer.
Considering my story above, are people giving you bad advice when they ask you to fake it till you make it? I would say that it depends. It is very bad advice in professions where skill and knowledge is the difference between life and death, I would not ask a doctor, or a lawyer to fake it till they make it, just think of all the people who may end up dead or in jail before they actually learn what they need to know. For professions that have a learning curve however, you may have time to learn on the job and so it may not be such a terrible life threatening idea.
Despite the fact of it not being life threatening in those instances, so much more positive things can be said for admitting your newness to a situation but your willingness to learn fast and hard. It definitely is easier to be exactly who you are and not constantly fear that you may be found out in one way or the other.
However it is still necessary to state that the underlying principle of faking it till you make it, which again I will state as confidence, is one that we would all benefit from inculcating in our professional and personal lives.
Bolster your courage, try out new and interesting things, get your legs firmly on the next wrung of the ladder, it is the only way that you will ever get to move forward.