I ask him/her something, I start to listen to the answer and all of a sudden I find myself thinking of something else or sleeping with the eyes open or looking at his/her way of talking, movements of lips and face. Sometimes, I start drowning in my own dreams or remembering something about the speaker, which is neither specific nor important.
Me, detaching from listening doesn't mean the topic or the speaker is boring but I just fall into this old habit. I feel sorry and then for making up, I say something that shows the things that were said interested me so much when the speaker finishes. I do that so even the person doesn't realize my temporary detachment and then I blame this playful mind and promise myself to be all ears next time.