Fake it till you make it is most associated with a salesman known as Glenn W. Turner and is different from the psychological concept known as "acting as if" in that acting as if means to emulate qualities that you don't actually have such as confidence, but fake it till you make it is a philosophy that encourages dishonesty in social interactions in order to project a certain lifestyle or talent that isn't actually there. Presenting yourself as a great investor while hiding losses would be an example of fake it until you make it. Presenting yourself as confident while being honest about your performance would be acting as if.
Fake it till you make it goes hand in hand with Ableism. The idea that you can do whatever you want, regardless of your limitations, just by changing what you believe and how you present. Nuerodyvergence isn't actually real, its just a mindset, so the thinking goes. It's a magical idea... but life is not a fairy tale.