Few things are refused outright. Mostly they are moved. "Later" is the word we use for the move, and it is a generous word — it sounds like a plan while asking for nothing.
The trouble is that later has no location on the calendar. A task sent there does not wait in an orderly queue; it drifts, and each drift makes the next one easier. By the time you notice, the thing has become a someday, and someday rarely arrives.
The remedy is not more discipline. It is a plainer question: if not now, then when, exactly? Give later a date and it becomes a decision again. Leave it undated and it stays a feeling, and feelings are easy to keep postponing.