Means of Ignorance

Here is a non-exhaustive list of commonly found means of knowledge that are invalid.

Delusions and irrational assumptions.

An assumption is a structure in the memory that is not founded on any evidence what so ever. A delusion is a firm belief is such assumptions. Blind beliefs, superstitions, dogmas etc. fall into this category.

People

Anything that is heard from parents, friends, people or society in general is invalid knowledge. Usually people are ignorant and are full of assumptions, so cannot be trusted with knowledge. Sometimes they are a useful means of knowledge as far as daily survival is concerned, but beyond that, there are only opinions.

Leaders

Most of them have an agenda to rule people, to keep them in control and to exploit them. Providing knowledge is not exactly their goal. Wealth and power is. So they employ all means to misinform people and keep them as ignorant slaves. Stupid masses can be easily ruled, can be easily commanded to kill others. People do not wage wars, competing leaders do.

Experts

Their agenda is to earn a living from knowledge of a certain field. If it gets more money, they are ready to take advantage of it. They usually have knowledge about a narrow field, and outside it they are completely ignorant.

Schools and universities

Form a part of the social, financial and political system. They are not meant for knowledge. They are meant for indoctrination and as a means to train people for jobs. The education system is usually under the control of governments, and they decide what 'knowledge' is and who needs it.

Media

Books, magazines, journals, tabloids, newspapers , encyclopedias, TV, internet, cinemas, documentaries etc. fall in this category. They are full of misinformation. Their agenda is to earn money by providing a bit of entertainment. There are some good books and content out there, as exceptions. However, an ordinary person neither understands them nor is interested in them. Most go for the cheapest. Written word is not an evidence, it is a matter of trust and blind faith on the writer.

At most these are a medium of information, which is simply a structure in the memory that points to knowledge, but is not knowledge.

Democratic beliefs

Or wisdom of masses, is the assumption that if many people are saying it, it must be the truth/knowledge. It is usually a majority opinion, which is mostly wrong and keeps changing with time, place, culture etc.

Time tested knowledge

Or ancient knowledge is sometimes surprising accurate, but most of it is now corrupted. The ruling class has taken special interest in corrupting it. It is a belief that if it is very ancient, it must be the right knowledge.

Authorities

Whatever these authorities say are their own opinions, and mostly they are trying to influence others via their position and reputation.

Institutions or traditions

Many claim to provide knowledge. They use their 'banner' and a lot of advertising to influence masses. Sometimes this knowledge is well hidden, and is never given away completely, or it is just theory or bookish knowledge. The agenda here is commercial, to gather as many students as possible, in order to sell them some 'knowledge'.

Information mixed with misinformation

This is by far the most dangerous means. Some knowledge is mixed with misinformation to make the whole of it appear valid. Generally masses, due to their impure intellect, as unable to discern the truth from false. Religions and politicians are found to use this method predominantly. And it is a very effective and time tested way to misinform and keep people ignorant.

Indoctrination

Planting ideas as 'truth and knowledge' in the immature minds of children is indoctrination. Usually they are too innocent to question any beliefs, and are easy to manipulate. The largest source of ignorance in humankind is indoctrination. Once these ideas take root in the early age, they solidify, and are almost impossible to get rid of. The agenda here is to manipulate people at a stage where they are totally helpless and defenceless. Children are an easy target. But even adults suffer from a good amount of indoctrination.

All these lead to ignorance, suffering, low intelligence and are a recourse of a lazy mind.