Everyone knows this dream: you dream you woke up, got out of bed, started the morning — and then the alarm rings for real, and it turns out you were asleep the whole time. In the dream you were fully certain you were no longer sleeping. Take the image further: a person falls asleep, in the dream lies down, dozes off once more, then "wakes up" — and is still inside that first dream. Sanskrit calls the waking state jāgrat and the dream svapna; and here is the striking thing: while in svapna you feel yourself in jāgrat, wholly convinced you are awake. Hence the sober thought: the very certainty "surely I, at least, am awake, I have understood it all" proves nothing — the sleeper feels exactly the same.