Focus your mind on each exercise. If your mind wanders you will not develop strength. Consider the laborer who works all day long. He is not as strong as the wrestler for he does not concentrate on his labor but thinks about other things.

From an article about Vyayam on the ChAoS & PAIN website (NSFW)

I don’t always do this… my mind sometimes is off on other things and I go through the motions. But when I focus intensely on each rep, that 1 focused rep is more useful than 10 unfocused.