Why is the Internal Editor such a problem?

The Internal Critic, aka Internal Editor, is the part of your brain that points out every single thing that is wrong with whatever you are doing (whether that’s writing or making a fancy dinner for your in-laws), brings up the obvious impossibility of whatever giant task you are required to do (whether that is writing a bestselling novel, finishing your Ph.D. thesis by the end of the month, or doing that three-month project your boss just handed you that they need by the end of the week), and...