Order one evening's events as drive-reduction theory describes them, from the bodily change to the return to baseline.

1. Her blood glucose falls below its set point, though she has not yet noticed feeling hungry.
2. The deficit registers as an aroused, uncomfortable state.
3. She feels restless and preoccupied, and cannot settle to anything until she eats.
4. She eats, and the deficit is corrected.
5. The restlessness fades and her internal state returns to its steady baseline.

The sequence separates two words that are used interchangeably in ordinary speech and mean different things here. The need is the physiological deficit - glucose below its set point - and it exists whether or not she notices. The drive is the aroused psychological state the deficit produces, and it is what she actually experiences as restlessness. Behaviour is directed by the drive, and the drive is caused by the need.

The last step is what the theory says everything is for: homeostasis restored, tension reduced, the organism back at baseline.

Which also shows exactly where the theory runs out. Follow this chain and every behaviour should terminate in a return to equilibrium - so the same person, entirely satisfied, choosing later that evening to watch something frightening or to walk somewhere new, is doing something this sequence has no room for.