Spontaneously

Impulsivity: This is a tendency to act on a whim, displaying behavior characterized by little or no forethought, reflection, or consideration of the consequences.

Automaticity: This is the ability to do things without occupying the mind with the low-level details required. It's usually the result of learning, repetition, and practice.

Serendipity: This term refers to events that happen by chance in a happy or beneficial way.