Concentration
Concentration is very complicated because you have to force yourself; it is tiring. Contemplation is a little better because you have a little more space to move. You are not moving through a narrow hole which is going to become more and more narrow.
Concentration has tunnel vision. Have you looked in a tunnel? From one side, where you are looking, it is big. But if the tunnel is two miles long, the other side is just a small round light, nothing else: the longer the tunnel, the smaller will be the other end. The greater the scientist, the longer the tunnel. He has to focus, and focusing is always a tense affair.
Concentration is not natural to the mind.
Mind is a vagabond. It enjoys moving from one thing to another.
It is always excited by the new.
In concentration mind is almost imprisoned.
In the second world war, I don't know why, they started calling the places where they were keeping the prisoners "concentration camps." They had their own meaning -- they were bringing all kinds of prisoners and concentrating them there. But concentration is actually bringing all the energies of your mind and body and putting them into a narrowing hole. It is tiring. Contemplation has more space to play around, to move around, but still it is a bounded space, not unbounded.
-Osho, ”From Misery to Enlightenment, #2“