“Enlightenment is the most important attainment in meditation practice, but deep insight is almost as important. It is said that once deep insight has been reached, it is certain that enlightenment will be attained. However, describing deep insight is a very delicate issue for two basic reasons. One is that there are three basically different ways that deep insight can develop, and there are innumerable variations of responses individuals have to this experience. The other is that if the descriptions of what happens are too explicit, then other meditators will mistake experiences they are having as being deep insight experiences.”
-Bill Hamilton, Saints and Psychopaths (emphasis added)

This paragrpah preceeds Sayadaw U Pandita's analogy of a line of ants on a wall. 

Revisiting this paragraph his mention of the 'three basically different ways that deep insight can develop' leapt out at me as I don’t recall registering it on previous reads. Nor do I recall seeing it referenced in other Progress of Insight sources, commentaries, or online discussions. 

What are the three?​​​​​​​

Just a personal conjecture, but considering that Hamilton refers to the A&P with his use of "deep insight" ("Deep Insight into the Arising and Passing Away of Phenomena"), one way to put into boxes what leads to crossing the A&P can be that it happens through either insight techniques, concentration techniques or practices that lead to energetic openings through routes that don't primarily cultivate attention skills, like drugs or bodywork.