What is the most difficult SD defense technique to learn?

Right now, I would say "verbal self-defense." I would say this for two reasons - 1) I am studying the art of verbal self-defense and 2) I am finding that the content of the studies applies to me.

Regarding number 2. I find that the discovery that I am as guilty of verbal attacks as any opponent is the hardest part to accept - I accept it. I also find that in order to use VSD I have to overcome my ingrained verbal assault tendencies. It was also important to note that like myself, my opponent does NOT fully recognize the fault. Makes it doubly hard especially since the most predatory verbal attacker tends to be the one closest to the victim where the bond of Love and Family ties close and tight.

It is so much easier to learn and teach how to clean someones clock when they verbally attack you yet to truly defend to your best you must deescalate/avoid. This means listening actively and recognizing the bait so you can respond with out resorting to the same tactics.

Truthfully, there are many things that are difficult to learn and most, if not all, tend to blend and mix making distinctions difficult to impossible yet it provides many benefits if patiently accomplished.

For me I discovered I had "placater, blamer, and computer modes of VSD." I find my opponent in one case to be "blamer and distractor" mode type. It seems many of us fall under the "blamer mode."