The first chapter ("Beginning Zen Practice") of Charlotte Joko Beck's book Everyday Zen offers a sharp distinction between productive mental activity and the usual tangled knot inside the mind:

There are two kinds of thoughts. There is nothing wrong with thinking in the sense of what I call "technical thinking." We have to think in order to walk from here to the corner or to bake a cake or to solve a physics problem. That use of the mind is fine. It isn't real or unreal; it is just what it is. But opinions, judgments, memories, dreaming about the future—ninety percent of the thoughts spinning around in our heads have no essential reality. And we go from birth to death, unless we wake up, wasting most of our life with them. The gruesome part of sitting (and it is gruesome, believe me) is to begin to see what is really going on in our mind. It is a shocker for all of us. We see that we are violent, prejudiced, and selfish. We are all those things because a conditioned life based on false thinking leads to these states. Human beings are basically good, kind, and compassionate, but it takes hard digging to uncover that buried jewel.

^z - 2014-09-10