Then comes dharana. After pratyahar, when a person has started coming back nearer home, coming nearer the innermost core. Pratyahar brings us near the gate; pranayam is the bridge from the out to the in. And then is the possibility of dharana, concentration. Now we can become capable of bringing the mind to one object. Note the logical flow of events here 1st, we gave direction to the body; then, direction to life energy -- now we give direction to our consciousness. Now the consciousness cannot be allowed to go anywhere and everywhere. Now it has to be brought to a goal. This goal is concentration, dharana: you fix your consciousness on one point it can be anything – your dream job, graduation, getting into medical school etc.
When consciousness is fixed on one point thoughts cease, because thoughts are possible only when your consciousness goes on wavering -- from here to there, from there to somewhere else. When the consciousness is continuously jumping like a monkey, then there are many thoughts and the whole mind is just filled with crowds -- a marketplace.
Dharana means the capacity to contain. Concentration is part of it. If you can remain with one idea for long, you become capable of the higher possibility of remaining one and the same for a long period -- because if you cannot remain one and the same for a long period, you will be distracted by the objects. A mind, which can remain in deep patience, can remain unmoving, only that mind can come to know one's own divinity. Plz note that it does not mean you become lazy…-:).
Bottom-line is – “ Successful people have one intention for a long period of time and people who are not successful have many intentions for short period of time”. Choose wisely…