Margen
In 1955, the British historian Cyril Northcote Parkinson formulated, half in jest, a law that now bears his name: work expands to fill all the time available for its completion.
If you're given a week for a two-hour task, the task will find a way to fill the week: you'll polish it, second-guess yourself, tweak it. Not because it needs it, but because the time was there.
The clever move is to flip it around: set yourself artificially short deadlines. Decide the report goes out today at five, that the suitcase gets packed in twenty minutes. A short deadline forces you to decide what matters — and almost everything else turns out not to.
It's not magic: it's taking away the space where work fattens up.