There’s no story without conflict, struggle. Ok, it’s also a principle. “I’d like to eat an apple” is just a description. If you add “the apple disagrees” you got conflict, then a story. Or maybe the apple is plotting revenge, or its family will hate me, or the apple is rotten.
The basic 3 act structure is recursive: beginning-middle-end. Stories are fractal-like. But I can see fractal aren’t atoms :) Emotion or desire are good candidates but not storytelling exclusive, so conflict is still my take because I cannot think of any other smaller unit.