leap in the dark

Translations
прыжок в неизвестность
He decided to leap in the dark and start a new business without any prior experience.
Он решил сделать прыжок в неизвестность и начать новый бизнес без какого-либо опыта.
Definitions
An action or decision made without knowing the possible consequences or outcomes; taking a risk based on little or no information.