I think what Pete Walker was saying is that it develops as a sort of hyper vigilance of your surroundings (in my experience, for example, something like guessing/keeping tally of all the things ourselves and others are doing wrong, much like the inner critic) that if your 4F response is Fight, will come out as outer critic. Otherwise it comes out more passive aggressively. But in my opinion it develops from a sense of hypervigilance (what could go wrong/what others are doing wrong) to self protect or deflect judgement (ie., My sibling did this thing so if I point it out the critical/unsafe eye is off of me for a time, etc.).