Sushi is an appetizing Japaneese dish, yet as the countless variations of it show, it doesn't achieve this feat through a single crucial ingredient. Traditionally prepared with seafood, vegetables, and wrapped in seaweed, each addition can be appropriately substituted or even removed while still preserving its signature flavour, but remove all and it vanishes. Sushi is greater than the sum of its parts - yet there is no "thing" that makes it delicious - it's through interaction of the mundane that the sublime emerges. Simultaneously, the sour-yet-slightly-sweet rice, as its' name "vinegar rice" would suggest, cannot be replaced.
The way the fish is sliced, the temperature, delicateness of the rice, the crispyness of the nori, fresh ingredients - these small, seemingly insignificant features compose to elevate it further.
All complex systems have their "vinegar rice" as well as the supporting elements.