Why don't people read instructions?

Some people are very careless when reading instruction on a work task they've been given or in reading any other kind of text. They would skip some of the sentences, not get deep into other and generally care very little if they understood the text right.

What is the common reason behind such behaviour - too little "cognitive capacity" or general disrespect towards other people/ egocentrism or too much dependence on emotional stimuli vs reasoning challenges or attention deficit disorder or simply low intelligence, etc?

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I doubt that there is a general explanation for this phenomenon and many factors are at play here. In the field of human factors the complacency effect has generated quite a bit of related research. This effect has also been termed learned carelessness. – crash Oct 31 '13 at 17:25
They have no time – Val Dec 4 '13 at 15:00

Multiple causes of not reading instructions

As @crash notes, there are likely many explanations for not reading instructions. It may be motivated by not caring about task performance. And such dispositions may be specific to the particular task or setting, or they might be partially related to some general disposition of the individual in terms of conscientiousness or skill.

The skill of not reading instructions

However, more generally, the concept of information reduction is related to skill acquisition. Haider and Frensch (1996) discuss the idea of how gradually over time participants start to ignore elements of a task that appear to be unrelated to task performance. So on one level, learning to ignore irrelevant information is a skill.

With regards to instructions, it is not always the case that reading an instruction manual is the most efficient means of achieving your goals. Trial and error, exploration, and so on are other strategies which often work quite well. In particular, many devices and software these days are designed to encourage people to explore. Likewise, it can often be a waste in learning information that may or may not be relevant, and so in some cases it makes sense to access instructions on an as needed basis.

It is also one thing to sit in the position of all knowing observer where you can know that in a particular case it would make sense to read the instructions over using an alternative strategy. However, from the actors perspective, they are in a sense operating without that knowledge. So they are in a sense averaging over their experience to form a decision about whether or not and in what detail to read the instructions. In some cases this will work out for the best, in others it wont.

General problem of task design

If you know that reading the instructions is particularly important in a given domain then you may want to alter the system or the task to encourage reading the instructions. Many organisations have compulsory training with a test in order to force users to learn certain information. Alternatively, you could make clear why reading the instructions is particularly important for this task. Similarly providing strong negative feedback when task instructions are not followed may help the individual to learn that in this domain reading instructions carefully is important. That said, it's often even better if you can incorporate human factors principles to design a system which is user friendly.

References

• Haider, H., & Frensch, P. A. (1996). The role of information reduction in skill acquisition. Cognitive Psychology, 30(3), 304-337.
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In my experience, there are people who like to follow instructions and those who don't. It's in their nature, they were born like this.
Some want to do the thing right, the way it was intended, not make mistake, and take most profit from it.
Some like to figure things on their own, push all buttons to see what does what.

Now regarding why people read badly when they read. I'll attribute this to the continuous and general decay of the modernized civilization. Compared to their parents and grand parents, people know less vocabulary, less grammar, have less concentration, less analysis skills, less dedication, and worst of all they don't care !

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Biological degradation of people by virtue of civilization? I have created a question to ask for the decay speed, biology.stackexchange.com/questions/7686 – Val Dec 4 '13 at 15:09
I meant intellectual. But there is biological decay as well. – user2534 Dec 4 '13 at 15:29
What is intellectual? Intellect is a combination of your biological giftedness plus cultural lessons. You say that the degradation is in their nature, they were born like this, which means that the factor in question is biological rather than cultural. Intelligence does exist alone, without biology and training as computer programs do not appear without programmers and computers. – Val Dec 4 '13 at 17:00
No no no, the fact that people like or not to read instruction is not a degradation. Only the fact that people are less and less intellectually skilled is degradation, and the root cause has to do with modern society. – user2534 Dec 4 '13 at 17:26