Here's why:

* Lever: A lever is a rigid object that pivots around a fixed point called a fulcrum.

* Venetian Blinds: The slats in a Venetian blind act as individual levers. When you pull the cord, you're applying force to the lever (the slat) to rotate it around its fulcrum (the point where it's attached to the blind).

While Venetian blinds also use other simple machine principles like pulleys to move the cords and wheels to rotate the slats, the primary mechanism of adjusting the slats is through the lever action.