In Charlie Beckwith's book about Delta Force [0] there is a line where he says (paraphrasing):
"The SAS never wanted to write down what their role was and what tasks they were trained for. Why? Because they didn't want to get pigeon holed into a role. ... They also never wrote down their SOPs b/c the argument was that 'if you can't keep it in your head, you shouldn't be in the Regiment'. At Delta, we were going to write down our mission AND write down our SOPs."
