In contrast, I believe nearly 100% of people who can keep five precepts and with no serious health problems can do at least a low quality first jhāna.
from an old post,
This is one thing I really haven’t been able to glean from the EBTs. How difficult is attaining jhana really supposed to be? Like how do you know that you really have each jhana factor as it is supposed to be according to the description in the suttas?
According to Vism.'s redefinition jhāna, one out of billion or one out of a million people who try can do it.
Vism. Chapter 12:
It is not possible for a meditator to begin to accomplish transformation by supernormal powers unless he has previously completed his development by controlling his mind in these fourteen ways. Now, the kasiṇa preliminary work is difficult for a beginner and only one in a hundred or a thousand can do it. The arousing of the sign is difficult for one who has done the preliminary work and only one in a hundred or a thousand can do it. To extend the sign when it has arisen and to reach absorption is difficult and only one in a hundred or a thousand can do it. To tame one’s mind in the fourteen ways after reaching absorption is difficult and only one in a hundred or a thousand can do it. The transformation by supernormal power after training one’s mind in the fourteen ways is difficult and only one in a hundred or a thousand can do it. Rapid response after attaining transformation is difficult and only one in a hundred or a thousand can do it.
kasina preliminary work: 1/100 to 1/1000
arousing visual nimitta: 1/100 to 1/1000
To extend the sign when it has arisen and to reach absorption is difficult: 1/100 to 1/1000
doing the math:
to get first jhāna, 1/1,000,000 to 1/1,000,000,000
one out of 1 million or one out of 1 billion.
The EBT paints a very different picture of the difficulty in attaining first jhāna.
step 1: replace all unskillful thoughts with skillful thoughts, such as metta (MN 19). MN 20 offers 5 useful ways to curb thoughts connected to 5 niv (hindrances).
step 2: Even if you can maintain a state of having just kusala thoughts 24/7, that condition alone is not enough for a first jhana experience. To be first jhāna, the frequency and intensity of V&V (thinking and pondering) have to be attenuated to a point that doesn’t hinder passsadhi-bojjhanga (tranquility awakening factor). both kāya (body of flesh and blood) and citta (mind) have to be deeply relaxed/calm/tranquil/passadhi for first jhāna to happen. Depending on health, age, and how charged your batteries are on that day, the bliss and happiness of the first two jhānas can feel anywhere from the spectrum of being “unusually comfortable”, to intense full body cosmic orgasm.
step 3: if that happiness and bliss can saturate most of your body (AN 5.28), for even the time it takes to snap your fingers (AN 1.53), that’s a first jhāna experience. In practice probably most people won’t trust their first jhana experience until they’ve experienced a decent 2nd jhana experience.
As for the lower boundaries of first jhana:
(1) SN 36.11 states speech ceases in first jhana. AN 5.26 shows various cases of how one would be using speech while in a first jhana context. You can hear an inspiring dhamma talk or mentally recite a dhamma passage with V&V (vitakka & vicara, thinking and evaluation), but if you open your mouth and vibrate those vocal cords, the energy flow outwards disrupts the physical bliss. This can be easily tested by one who can do 2nd jhana.
(2) 5 niv (hindrances) have been temporarily supressed, especially kāma chandha, the hindrance of sensual desire for the 5kg (sensual pleasure strings).
AN 9.41 gives a good description of the Buddha struggling to learn first jhana and what condition knocked him out of it:
“Before my enlightenment, while I was just a bodhisatta, not yet fully enlightened, it occurred to me too: ‘Good is renunciation, good is solitude.’ Yet my mind did not launch out upon renunciation and become placid, settled, and liberated in it, though I saw it as peaceful. It occurred to me: ‘Why is it that my mind does not launch out upon renunciation and become placid, settled, and liberated in it, though I see it as peaceful?’ Then it occurred to me: ‘I have not seen the danger in sensual pleasures and have not cultivated that [insight]; I have not achieved the benefit in renunciation and have not  pursued it. Therefore my mind does not launch out upon renunciation and become placid, settled, and liberated in it, though I see it as peaceful.’
352“Then, Ānanda, it occurred to me: ‘If, having seen the danger in sensual pleasures, I would cultivate that [insight], and if, having achieved the benefit in renunciation, I would pursue it, it is then possible that my mind would launch out upon renunciation and become placid, settled, and liberated in it, since I see it as peaceful.’ Sometime later, having seen the danger in sensual pleasures, I cultivated that [insight], and having achieved the benefit in renunciation, I pursued it. My mind then launched out upon renunciation and became placid, settled, and liberated in it, since I saw it as peaceful.
353“Sometime later, Ānanda, secluded from sensual pleasures … I entered and dwelled in the first jhāna. While I was dwelling in this state, perception and attention accompanied by sensuality occurred in me and I felt it as an affliction. Just as pain might arise for one feeling pleasure only to afflict him, so too, when perception and attention accompanied by sensuality occurred in me, I felt it as an affliction.
As you can see, the EBT passages on first jhana are vastly different than the VRJ ( Vism. redefined jhana of Vism. and later Abhidhamma).
If you can smile based on a kusala thought, like doing an act of kindness for a stranger, or even just thinking kind thoughts to anyone, to they point where you smile, feel comfortable, maybe your heart/chest area feels warmer and your skin tingles, that’s enough kaya passadhi and citta passadhi to give you a taste of first jhana.
IMO nearly 100% of people are capable of experiencing at least a low quality first jhana.
The remaining 3 jhanas requires an ability to deeply relax and sustain that. But once you know the trick of it it’s really easy. The difficulty of first jhana and 2nd jhana are qualitatively different. 2nd jhana also requires the energy channels to be very open, and that will be dependent on health condition. Even if you’re doing the proper technique, until those channels open, you’ll be stuck in jhana constipation mode for some time.
Someone keeping 5 precepts well should be able to do first jhana. For second jhana, you’ll need 8 precepts and brahmacariya, to build up the internal energy. When the internal energy accumulates enough, you’ll have enough heat and force to melt the blockages in your energy channels.
IMO, nearly 100% of people who are willing to commit to the practice 24/7 should be able to at least stumble into a momentary 2nd jhana occasionally, for example when they lie down to rest and finally stop thinking to deeply relax the body and mind.
I wasn’t born with any special samadhi talent, and my jhana came slowly, over years. If I can do it, anyone can do it. The only thing I’m different than most people is that I had this attitude and mindset: I am a son of the Buddha. The noble eightfold path is my inheritance, my refuge, my raft. I’m going to watch over my raft 24/7. Jhana is my birthright. I’m going to get it no matter how long it takes, how much pain I have to go through, I’m going to get it or die trying. Now in hindsight, jhana didn’t require any physical pain. It does require resilience and not giving up though, because jhana constipation can last a long time. Most of the difficulties in the journey came from the misinformation in Visuddhimagga and the doubts and wrong practice that it sidetracked me with.