Gidden's Duality of Medium and Outcome

Accorinding to Giddens, social structure is both medium and outcome. Structure influences actions at the same time it is constituted by them.

From Giddens 1979:70:

Every process of action is a production of something new, a fresh act; but at the same time all action exists in continuity with the past, which supplies the means of its initiation. Structure is this not to be conceptualized as a barrier to action, but as essentially involved in its production, even in the most radical processes of change.