What differentiates smart people and dumb people or idiots?
It is the power of common sense, a keen eye to observe things, validate what they hear or read, not take things for granted. It is about application of mind on simple things and not doing things blindly or mechanically. A lot of graduates know or taught only doing tasks and not application of mind. Over a period of time and a lot of skulduggery of their bosses and by learning from mistakes they become wise and start using common sense. They start perceiving information and how to relate it to what they already know. But some people are unwilling to learn or disinterested to learn and are sometimes pre-occupied with other than office work to continue being ignorant and committing a lot of errors and blunders at which point in time they are either given lesser responsibilities or are forced to leave the organisation.
A major part of the ability to think on things and apply their minds and be conscious of the environment and data while performing a task or taking a decision is dependent on the way the people are brought up during their schooling or college days. The environment, the people and the projects that encourages them or forces them to think through things is the key to understand how things work and what things affect and how they affect a certain object/objective. This enables them to do a self check with readily available knowledge/information in their head to understand the trade offs and take a decision or perform the task right in the first instance.
Curiousity is another factor that enables people to learn and apply their minds. Curiousity also leads to creative thinking and adds value to things and brings about new solutions. Curiosity too is a factor that has to be encouraged in the childhood and cannot come suddenly at an old age. This factor in turn can be identified and leads to a talent.
Determination helps people focus. Another key factor that avoids innumerable distractions and stops others needs taking over your identified goal. This also allows people to bring more of their resources (time, money, connections, etc.) to the goal instead of using their resources to do other things.
So, to be smart and use common sense, encourage people to increase their curiosity and help them achieve their goals for them to see the value of their goals achieved through determination.