Spontaneousness is when something happens without being planned or thought about beforehand.
Spontaneousness is usually seen as a good thing because it can make life more fun and interesting.
Examples:
Her spontaneousness made the party more fun.
I like the spontaneousness of his jokes.
The spontaneousness of the picnic made it more enjoyable.
The spontaneousness of the dance party surprised everyone.
The spontaneousness of the trip made it an adventure.
The spontaneousness of the decision made it memorable.