Thrownness (German: Geworfenheit) is a concept introduced by German philosopher Martin Heidegger to describe the interactions of the subject with its surroundings in the everyday life, that causes it to act upon instincts, immediate reactions to other people's language and actions, "flow with the situation," and immediate interpretations.
Once one accepts that to not act is also an action, Heidegger notes that one is 'thrown' into situations without being able to reflect on them first, for to reflect on them (not act) is also something that can be interpreted as an action. One therefore must rely on instinctual interpretations, and go with the flow.