“The Progress of Insight,” or a series of experiences obtained during long, intense meditation practice – which culminates in Nirvana – is a taboo subject.

Many American meditation teachers don’t usually discuss it with their students. Some who say they have experienced it believe it’s a personal, private matter not to be shared. Others struggle even to describe what the experience was like for them.

Steve Armstrong, a longtime meditation teacher and co-founder of the Vipassana Metta Foundation, sat down with ABC News’ Dan Harris for his livestream/podcast show, “10% Happier with Dan Harris,” to discuss in-depth what “The Progress of Insight” means and whether nirvana, or what’s known as the “unconditioned,” is actually possible -- though Armstrong says he has achieved it for himself before.

“The first visit to the unconditioned is a profound condition. It permanently transforms the mind,” he said. “You still realize that nothing is going to do it for you that hasn’t been done before but your understanding of what happiness is forever changed.”

Watch the full interview in the video player or download the "10% Happier" podcast iTunes.

Armstrong, who practiced as a monk in Burma for five years in the '80s, is the managing editor of a new book project that translated Mahasi Sayadaw’s “Manual of Insight,” out in stores and on Amazon on May 17. The book is sort of an user’s manual for “The Progress of Insight,” or how to be enlightened through insight meditation as written by Mahasi Sayadaw, a renowned Buddhist monk.

As Armstrong says, the progress towards Nirvana is an adventure –- one that includes periods of both intense bliss, and also intense fear.

“As you become familiar with how the mind works, and you see how the mind works, it’s not what you think about yourself, it’s what your life actually is, that’s important,” Armstrong said. “Once you start looking at that and you start seeing how the mind works then you can start putting aside some of the reactivity, some of the recreational distractions that you indulge in, and actually see the mind.”

There are 16 “steps” or “knowledges” in the “Progress of Insight” achieved through meditation. The First Knowledge, Armstrong explained, is basic awareness, waking up to the fact that we exist.

“There’s a lot of times that we’re just living life and we don’t know what we’re doing...we’re on automatic pilot,” he said. “[First Knowledge] is when you come out of automatic pilot and you think, ‘this is what’s happening to me,’ breathing in, breathing out, walking down the street. Oh, hearing sounds, getting angry, getting excited, feeling bliss, whatever.”

The Second Knowledge is the knowledge of Discerning Conditionality, or realizing that things are not happening around you at random but that there are “causes and conditions” to everything. Next is the knowledge of the “three marks of existence,” impermanence, suffering (or “dukkha”) and non-self or selflessness.

This is where “you start to recognize the quality of your experience,” Armstrong said, and realizing “our mind is kind of out of control,” and that “we don’t control all the conditions of our life externally or internally.”

The Fourth Knowledge is the “arising and passing away,” which is when recognizing moments or objects are coming to your mind and passing through very quickly and “you’re not stopping the flow of experience to have a reaction to it or have a relationship with it, or cognitive story about it. The mind is just seeing things as the go by very rapidly,” Armstrong said.

This experience, he added, can cause “pseudo nirvana” or “spiritual goodies,” where the body and mind feels a moment of incredible bliss and you think you’re enlightened.

But then you come to the next stage of practice, which is when you realize that it’s hard to keep track of these moments as they fly by in your mind. In this stage, Armstrong said people can feel lost and eventually “there’s fear and disillusionment” from not feeling fulfilled by life anymore, which is why he stressed that having a good teacher is a must.

But for those who can get through what some call the “dark night phase,” there is “re-observation,” or reinvesting in getting back on the path towards enlightenment, where we recognize everything that arises in our consciousness without getting caught up in it.

“The spiritual goodies arise because you’ve had good practice but as soon as their arise they become an object of indulgence or feeling gratified,” Armstrong said. “It’s the gratification of those experiences that’s the corruption. Joy is not a corruption, tranquility is not a corruption. Faith is not a corruption, indulging and clinging to them is.”

From there, when the mind “doesn’t want to reach for what it sees,” Armstrong said, meaning you can recognize the feeling in front of you without attaching to it, that’s when people can enter the “unconditioned.”

“I can’t show it to you, but the experience of it is real,” he said. “Once you taste the experience of the unconditioned, you know what it is.”

Watch the full interview in the video player or download the "10% Happier" podcast iTunes.