For a being who has entered the stream, One might get caught up with outside/worldly things. When this happen, the dhamma/path will become blur. But once they remember the path again, then one can bring the sati/samadhi back, the path will become clear again.
Buddha explained it on SN 55.40:
And how does a noble disciple live negligently? Firstly, a noble disciple has unshakable confidence in the Buddha, Dhamma, Sangha, and …
They’re content with that confidence, and don’t make a further effort for solitude by day or retreat by night. When they live negligently, there’s no joy. When there’s no joy, there’s no rapture. When there’s no rapture, there’s no tranquility. When there’s no tranquility, there’s suffering. When one is suffering, the mind does not become immersed in samādhi.
When the mind is not immersed in samādhi, dhamma does not become clear. Because dhamma has not become clear, they’re reckoned to live negligently.
Live negligently here means one didn’t practice dhamma diligently, one attends to worldly things: working, family life, etc.
A stream enterer and once returner haven’t fully developed samadhi/sati. So when they died, they could forget about the dhamma/path. But when the condition is there, stream enterer and once returner will remember back the dhamma/path again. Then they can continue the path. This explained in one of the Sutta, AN 4.191.
Take a mendicant who memorizes the teaching—statements, songs, discussions, verses, inspired exclamations, legends, stories of past lives, amazing stories, and classifications. They’ve followed those teachings by ear, reinforced them by recitation, examined them by the mind, and well comprehended them theoretically. But they die unmindful and are “reborn” in one of the orders of gods. Being happy there, passages of the teaching come back to them. Memory comes up slowly, but then that being quickly reaches distinction. This is the first benefit you can expect when the teachings have been followed by ear, reinforced by recitation, examined by the mind, and well comprehended theoretically.
On the other hand, non returner and arahant are not possible to forget due to their samadhi/sati is fully developed.
How did Buddha become awaken?
You will find many reference in sutta how Buddha become awaken such as MN 85:
‘I recall sitting in the cool shade of the rose-apple tree while my father the Sakyan was off working. Detached from sensual pleasures, Detached from unskillful qualities, I entered and remained in the first jhana, which has the rapture and bliss born of seclusion, while vitakka vicara is present.
Could that be the path to awakening?’
Stemming from that memory came the realization:
‘That is the path to awakening!’
There are many more Sutta about this. So one might need to review it all to fully understand.