I have observed my wandering mind and have detected the role of desire in my getting caught up with the topics that pop up.
Let's suppose I am meditating and I start to wonder if the change I got at the store today was correct. I start calculating the difference between what I gave the clerk and what I received back with my purchase. Then I remember that I am supposed to be meditating. I should let it go, right? I note "calculating, calculating, calculating..." and the calculating stops (if for no other reason than that the energy involved in noting takes away the energy required to obtain an answer). However, let's suppose I really want to know the answer and so I continue calculating until I get the answer. When I get the answer I may be relieved (I did get the right change after all), which is what I hope will happen, or not (the clerk made an error or, perhaps, intentionally cheated me). The critical point in the process is when desire gets the upper hand and prevents me from letting go. What ties me to the calculating is the desire to get the answer, and, with it, to provide relief that I did get the right change or, alternatively, to confirm my suspicion that I did not get the right change.
Planning is probably one of the most common afflictions of meditators. Substitute planning for calculating in the example. The same process takes place. It is the desire to resolve things, to have a good plan, and the relief that we think it will bring, that gets us caught in planning while we meditate. To let go of planning we should note it. However, more importantly, we should see behind it the desire to resolve things, to get to the plan that will solve all problems, to get to the peace of closure. Meanwhile, we get caught up in and spin around with planning and forego the peace of being focused and mindful at the present moment.