Some time after the end of the last ice age, say 12,000 years ago, some human groups of hunters and gatherers began to settle down and farm plants and animals, and to live in settlements of increasing size and complexity.
That's the standard idea. But what if they had started earlier, during the ice age itself? What if the earliest such settlements were in the fertile river deltas, or along the flat shores of present-day China, Indonesia, South Asia, the Middle East, or the Gulf of Mexico?
That would have been unfortunate. As the icecaps melted, sea levels rose hundreds of feet, sometimes gradually, sometimes in a catastrophic event in which earthquake, tsunami and irreversible coastal flooding were combined.
That kind of event would destroy any nascent civilization, destroy all the artifacts of technology, destroy all the tools for recreating the life they had, destroy most of the population, and make scattered refugees in an unfamiliar landscape of some random survivors with their random skills. As that generation died out, not all the skills would have been transmitted properly, because the conditions for training and practise would not be appropriate.
Perhaps, over a period of hundreds of years, their descendants would reestablish the understanding of early farming, herding, construction, astronomy, mathematics, simple metalworking, whatever had been lost; and we, today, would naturally think they were developing it for the first time.
Because the oldest neolithic archaeological remains may not yet have been found, if they are two hundred feet underwater, and covered by a hundred feet of silt.