“Operating inside an opponent’s OODA loop” is Boyd’s primary device for dealing with opponents (he has other recommendations, primarily at the grand strategic level, for relationships with our own side and the uncommitted). He suggests its power in several places. Here’s probably the best known, from Patterns of Conflict:
And then later, in Strategic Game, where he places the concept into the “strategic game” of interaction and isolation:
Interesting theory, but what happens in real life? Pretty much the same thing. Here’s an observation by a former senior member of the Afghan government on the April 21, 2017, attack by the Taliban on an army base in the northern part of the country:
“The enemy has the strength — they have more people in their units now — and the speed of action,” said Rahmatullah Nabil, the former head of the Afghan intelligence service. “Unfortunately, we have slowed down our decision-making.” From the New York Times, “‘A Shortage of Coffins’ After Taliban Slaughter Unarmed Soldiers.“
Note that this comment could operate at not only the tactical level — how a force of 10 Taliban successfully attacked a major base — but also how the strategic situation in the country appears to be continuing to deteriorate.
Boyd never explicitly defined “operating inside the OODA loop.” Perhaps the closest he came was at the top of the left column on Chart 132. I don’t know whether he considered the concept to be self-evident, or whether he was using the classic Zen technique of pointing, rather than explaining.