The phrase "Fake it until you make it" may work concerning matters that only require conversation and appearance, but when it comes to demonstrating value it is impossible to make it faking it. For example, lets say you are asked to electronically pull together the evidence in a case using a popular legal technology program like Summation or Trial Director. A winning smile, firm handshake, and calm composure will not allow you to complete this task without knowing how to use these particular programs. You can fake it while you call on friends, co-workers, and read through instruction manuals, but when your managing attorney realizes that it took you three times as long to complete the project than what was expected that winning smile may turn into a frown as you are handed a pink slip.
Confidence is one thing that your career can not do without. It is essential for everything you do from interacting with clients to presenting your ideas to colleagues and supervisors. It is not what you learn by taking legal education but by understanding your worth and value. It can not be faked or feigned, but it can be practiced.
Instead of faking confidence which will only allow you to land a new job, promotion, or raise but not allow you to keep it, do what is necessary to build your confidence by actually knowing and mastering your job and career.