Observing thoughts is like registering words without trying to understand what is being said. If we’re talking to someone, we want them to listen to us, not observe us. Listening requires relinquishing control, allowing oneself to enter another world – to be taken into that world. To follow the sprites. Listening involves a lot of non-listening - attention to something other than the just the words: gestures, facial expressions, inflections, interpretations of what we’re hearing, inchoate reactions, incipient responses partly rehearsed.
All this happens very quickly, on the order of seconds and milliseconds, much of it non-verbal. Thanks to echoic and working memory, and a speed of cognitive processing faster than the speed of talking, we can still do a pretty good job of following what somebody is saying even though our attention is not always fastened on the words. So it is with listening to our thoughts: they speak and we weave in and out of listening to them, weaving out being just as important to understanding, learning, accepting, rejecting, appreciating, inferring, having one's assumptions tested, realizing an unknown that had been an unknown unknown, and all those other happy accidents made possible by a mix of control and surrendering control that enriches our lives.
Going astray is part of the risk of yielding. We try to control risk by pulling back and "observing" but there is no movement without being sucked in.