Nobody knows but the person who has realized it that there are some rifts in practising concentration. The first fire of us will be burnt out by infiltration of thoughts. Our whole span of concentration endeavor is tattered by thoughts in one way. Concentrate means to flow all thoughts in one way – FOCUS, or only one thought. Our main issue is to bring down the number of thought to one and then to nullify it to zero (Why should we nullify it to Zero? For answer please read my coming days’ story). It is called meditative state or Meditation. Only then our story or Meditation will start. We are strengthening our Observation Power to keep away such creeping in thoughts. It was, as I found the hardest task in the world. If you like to take challenge, you can take this challenge which will benefitted you in due course. To evacuate Mind, let the thoughts go out. Try some better exercises or Yogas. Be sure that if there is a problem, there are solutions too.