Agnoiology is the study of ignorance. More specifically :

The doctrine of things of which we are necessarily ignorant" ref.^{[ paywalled ]}

In other words. the opposite of epistemology which is the study of knowledge.

Given that human intelligence has limits, and that we have not explored the entire universe, it's a given that the extent of human ignorance is currently unknown.

There are a plethora of reasons why ignorance occurs and persists. Some examples (in no particular order) :

• lack of resources and/or equipment
• insufficient previous knowledge to build on
• incompatible physical scales (too large, too small)
• incompatible timescales (too short, too long)
• fear of the unknown (example ref.)
• cultural pressures (the study of which is known as Agnotology)
• insufficient intelligence
• failure to recognise unknown factors (example ref.)
• laziness
• lack of curiosity

Note that Agnoiology also covers subjects which are by their nature unknowableplugin-autotooltip__plain plugin-autotooltip_big#Unknowable

Pages with this tag are about concepts or entities which, by their nature, can never be accurately described.

See :. An example would be trying to definitively classify a growing sequence of numbers as randomplugin-autotooltip__plain plugin-autotooltip_bigRandom numbers

unknowable

"We can never decide for sure that a number is random, but what we can do is apply an increasing number of tests and treat our sequence of numbers as innocent until proved guilty."

Source : Prof. Colva Roney-Dougal, senior lecturer in Pure Mathematics at the University of St Andrews, speaking in - given that the next digits may start repeating.