It's very rare that I have an interesting thought during Zazen. Usually I'm either trying to just stay upright or just letting go of a stream of random nonsense. But tonight, as I found myself inside a particular train of thought, I suddenly realised that I could jump off the train. And also, that the feelings that accompanied those thoughts would not be there forever. "You won't always feel like this" I thought.
That's a common thing for me: getting caught by stuff which a bit further down the line seems totally unimportant.
Maybe it's good to try and see a problem from your future.