People are mentioning levers, but it is important to see here that you actually have one. Your setup is similar to a claw-hammer or so: a rigid object with three points $A,B,C$ in a line in that order, such that $C$ is lying against some surface and thus acts as a center of rotation, some force is connected at the other end, $A$, and the force is amplified on the “nail” that is wrapped by the claw in between those points exists at $B$.
Lesson: it is very tempting to take $B$ as a pivot, or a center of rotation, but the choice of what you select as your center of rotation is actually very arbitrary, and the physics of torques works well no matter what you choose. If you have multiple places that are stationary on an object, even if one of them seems more correct than the other, sometimes it is helpful to imagine the other as the pivot and see if that looks interesting.
For example, very often to figure out the force direction on a point of contact, it is helpful to imagine what would happen if that point was not there. The bottom hinge of a door pushes the door out from the frame and is under compression; the top hinge pulls it in towards the frame and is under tension. I can say this very confidently because I can say “if that top hinge weren't there it would rotate around the bottom hinge away from the frame” and “if that bottom hinge weren't they it would rotate around the top hinge into the frame.” This freedom is very helpful.