"Hidden Divergence" is an obscure term that has become part of the vernacular but does not (I believe) originate with Dana. Meaning, it isn't something to worry about at this point. You really need to start at the beginning and study, study, study. And then do it all over again. It's the only way to learn, which begins with the basics. (but FYI the hidden divergence refers to the green and gold lines that attach to the DB along with the magenta and sky blue--frequently "behind" them).