[Trissinas]

The tenth and last defilement is Ignorance. This covers every kind of defilement not yet mentioned. The word "ignorance" refers to a condition of lack of knowledge, and in this case "knowledge" means real knowledge, correct knowledge. Naturally no creature can exist without having some knowledge, but if that knowledge is false, it has the same value as no knowledge. Most people suffer from chronic ignorance or false knowledge; most of us are benighted. The most important questions for human beings are those that ask: "What is suffering, really?," "What is the real cause of the arising of suffering?," "What is real freedom from suffering?" and "What is the real way to attain freedom from suffering?" If some individual has real knowledge, if he is free of ignorance, he is reckoned as enlightened. The totality of human knowledge is of untold extent, but the Buddha classed most of it as not essential. The Buddha's enlightenment encompassed only what need be known. The Buddha knew all that need be known. The word "omniscient" or "all - knowing" means knowing just as much as need be known: it does not include anything non-essential.
buddhadasa