What is your mind doing when it leaves the room?
What it argues
Mind-wandering is not a lapse but a large share of waking thought: self-generated, often future-directed, and only partly under control. The review separates deliberate from involuntary wandering, which matters. Deliberate wandering is where planning and writing happen. Involuntary wandering is where rumination lives.
The probe
Three alarms a day for three days. At each, label the last five minutes: on task, deliberately elsewhere, or hijacked.
The source
The Science of Mind Wandering, Annual Review of Psychology 66 — Jonathan Smallwood and Jonathan Schooler, 2015. The link goes to the text or to a catalogue record for it, not to a summary. This one is a catalogue record: the entry gives you the question and the probe, not the argument in the author's words.