Today is the first cheat day - that is, I kind of cheated in coming up with a q-themed title. Usually, this concept is referred to as fast-slow processing. But close enough, right?
Basically, your thought processes can be divided into two types: fast (quick) and slow. There are a few different theories about these different processes, but they're all categorized as "dual process theories." The two big ones are Chaiken's Heuristic Systematic Model and Petty and Cacioppo's Elaboration Likelihood Model (which is actually a model of persuasion). Additionally, Kahneman calls them "intuition" and "reasoning."
As I've blogged about before, we're cognitive misers - mental energy is a fixed resource and so we save it for the times we really need it. So we tend to go through life on auto-pilot, processing things quickly and with as little effort as needed. In Chaiken's model, we call these heuristics, which are quick categories or mental shortcuts. What feels good or makes us happy? What do we usually do? This is great if you're deciding, for instance, where to go for lunch.
In Petty and Cacioppo's model of persuasion, this is called the peripheral route. We may choose to believe someone because they have a higher degree or are attractive. Persuasion occuring on this route is often temporary. We may be persuaded in the moment, but that attitude change is not likely to "stick." You may have experienced a time before when a friend is persuaded to a new way of thinking, and vehemently expresses that new attitude, only to fall back to their old way of thinking.
The other route is systematic. We think really hard about what we want, employing logic and reason, as well as emotions, to come to a conclusion. In Petty and Cacioppo's model, this is called the central route. We think critically about what the person trying to persuade us is saying and doing, and come to our own conclusions. Persuasion occuring through this route is more long-term. We may have a permanent, or nearly permanent, change in attitude.
Which route or approach we take depends on two things: ability and motivation. We must be able to think critically or systematically about something in order to do that. Therefore, a person with higher intelligence is more likely to engage in central route or systematic processing.
But - and there's always a but - we must also have the motivation to do so. Two people may be of different levels of intelligence, but if the high intelligence person is unmotivated to think critically, s/he won't look much different than the low ability person. Because we're cognitive misers, we tend to function at low motivation for thought.
Now, there are some people who are more motivated to think systematically than others. We call these people "high need for cognition." Those are the people who, for instance, go through all the pros and cons about different lunch options before making a decision. They will still use heuristics or peripheral route processing on occasion, because even though their motivation is high, their ability might be low moment to moment if they've expended a lot of cognitive resources. But because high need for cognition people tend to have higher baseline ability, they have more resources to work with, and it takes them longer to exhaust those resources.
It's important to point out that decisions made using heuristics or peripheral route processing are not necessarily wrong. You may, for instance, choose to believe a person because she has a PhD in a topic, without really processing what she has to say. But another person who thinks critically may also believe the person and be persuaded, because of the strength of the arguments. And there are certainly times when systematic thought is unnecessary.