Observation implies no accumulation of knowledge, even though knowledge is obviously necessary at a certain level: knowledge as a doctor, knowledge as a scientist, knowledge of history, of all the things that have been. After all, that is knowledge: information about the things that have been.
There is no knowledge of tomorrow, only conjecture as to what might happen tomorrow, based on your knowledge of what has been. A mind that observes with knowledge is incapable of following swiftly the stream of thought. It is only by observing without the screen of knowledge that you begin to see the whole structure of your own thinking. And as you observe—which is not to condemn or accept, but simply to watch—you will find that thought comes to an end.
Casually to observe an occasional thought leads nowhere. But if you observe the process of thinking and do not become an observer apart from the observed, if you see the whole movement of thought without accepting or condemning it, then that very observation puts an end immediately to thought—and therefore the mind is compassionate; it is in a state of constant mutation.
The Collected Works vol XIII, pp 299-300