Quick. I want you to say aloud what color you see in every word in the chart to the right. Do not say the word you read. 
(For example, sometimes the word "white" will be in the color red so you would say "red.") The quiz, better known as the Stoop task, is a classic psychology experiment and is used in neuropsychological evaluations to measure mental vitality and flexibility.
It is best done with another person observing you because you won't always catch your own mistakes. The reason this simple exercise is so difficult is because reading a word is an automated task and takes relatively little mental effort. Naming the color of the word, however, requires concentrated and deliberate thought.
In many ways the act of learning is similar to reading words — it can become an automated process requiring little effort. For example, think of reading an article in a scientific journal or an opinion piece in the commentary section of your favorite newspaper. In many cases all you are doing is either adding new knowledge to your existing base of knowledge or reconfirming an existing viewpoint you have previously learned. (This isn't an inherently bad thing but if your base of knowledge is becoming obsolete or if your viewpoint is based on biased information it isn't helpful.)
Unlearning, like the naming of the color of the word, is more difficult. It requires deliberate thought and forces you to ignore the "obvious" answer. This act of ignoring the "obvious" answer can often be the first step down the difficult, albeit rewarding, path of unlearning.
Interested in other unlearning exercises? Check out these past posts:
To Unlearn: Try a Blind Taste Test
