When you concentrate, whether you are in your mind or in your heart or in your entire being, think of the whole world as smaller than the smallest. Just feel that the entire world is tinier than the tiniest. Then your mind will not act like a vagabond or a stray dog. If you take the world as something very vast, then your concentration can never, never be effective. But if you take the entire world as a tiny thing, absolutely as small as your fingertip, then your concentration will be most powerful.
For concentration, everything has to be smaller than the smallest. Otherwise, our eyes will be roaming from this side to that side and our concentration will go away. We will not be able to focus; we will not be able to penetrate the object of our concentration. If you are lifting weights, whether it is 90 pounds, 100 pounds, 120 pounds or 200 pounds, do not think of the size of the weight. Just take the whole object that you are lifting as absolutely smaller than the smallest. Whenever you concentrate on something, you have to feel that that particular thing is very, very tiny. On the strength of our imagination, we make the object of our concentration extremely small.
For meditation, it is just the opposite. We have to imagine something as large as possible. On the strength of our imagination, we meditate on something vast. Meditation is vastness, while concentration has to be focused on the tinier than the tiniest object to be successful.