Thought arising

I often hear it being said that with meditation/mindfulness we observe the thoughts and feelings coming and going but I'm not sure if this is a clear explanation of what occurs because in my experience of practicing for over 6 years I don't think I have ever actually seen a thought arising. What happens with me is that I recognise that my mind is lost in a thought and once I do then the thought ends. This is different to noticing the arising. So I'm following breath, lost in thought, come back to breath, lost in thought etc. I can intentionally say to myself "ok now I'm going to think about ...." And in this way I can observe the process of thinking but unless I do this I don't see how its possible to see a random thought arising. Is this correct? If this is not correct then why in 6 years can I still not do this? The recognition of random thought is always in past tense.