What is the meaning of Narrow?
Just an indication of the brief moments when understanding is present. There are so many wrong paths and only one right.
This is the only way, monks, for the purification of beings, for the overcoming of sorrow and lamentation, for the destruction of suffering and grief, for reaching the right path, for the attainment of Nibbana, namely, the four foundations of mindfulness
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https://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.045.than.html
“What do you think, Ananda: Which is harder to do, harder to master — to shoot arrows through a tiny keyhole without missing, one right after the other, or to take a horsehair split into seven strands and pierce tip with a tip?”[1]
“This, lord, is harder to do, harder to master — to take a horsehair split into seven strands and pierce tip with a tip.”
"And they, Ananda, pierce what is even harder to pierce, those who pierce, as it actually is present, that ‘This is stress’; who pierce, as it actually is present, that ‘This is the origination of stress’… ‘This is the cessation of stress’… 'This is the path of practice leading to the cessation of stress.
vis. XVI 85
As long as a man is vague about the world,
About its origin, about its ceasing,
About the means that lead to its cessation,
So long he cannot recognize the truths