The present invention relates to an assembly for insertion and retention of a fastener in tissue or bone comprising a staple comprising a first arm, a second arm, and a bridge extending from, abutting, or adjacent to a proximal end of first arm and a proximal end of second arm, wherein the first arm includes a first trunk portion extending for at a least a portion of the length of the first arm and the second arm includes a second trunk portion extending for at least a portion of the length of the second arm, wherein the first trunk portion has a lateral extent that is larger than a lateral extent of a non-trunk portion of the first arm and the first arm includes a first change in lateral stiffness disposed where a distal end of the non-trunk portion of the first arm abuts the first trunk portion, wherein the second trunk portion has a lateral extent that is larger than a lateral extent of a non-trunk portion of the second arm and the second arm includes a second change in lateral stiffness disposed where a distal end of the non-trunk portion of the second arm abuts the second trunk portion, wherein each of the first trunk portion and second trunk portion include at least a first projection and a second projection, wherein the first projection on each of the first trunk portion and the second trunk portion includes a first proximal surface extending away from the respective trunk portion in a first direction and the second projection on each of the first trunk portion and the second trunk portion includes a second proximal surface extending away from the respective trunk portion in a second direction different from the first direction, such that a pullout force applied to the bridge causes rotation of the first trunk portion at about the portion where the first change in lateral stiffness is disposed and causes rotation of the second trunk portion at about the portion where the second change in lateral stiffness is disposed and increases a holding force with increas
