Fracture and buckling of slender structures are typically regarded as a first step towards failure. Instead, we envision mechanical instabilities in structures as opportunities for scalable, reversible, and robust mechanisms that are first to be predictively understood, and then harvested for function. I will first show how delamination and fracture cooperate in thin films leading to the propagation of robust fracture patterns that offer opportunities to use cracks as a tool to design surfaces at small scales. I will then focus on thin elastic shells to revisit the canonical mechanics problem of sensitivity of shell-buckling to geometric imperfections. Finally, I will move on to the post-buckling regime of shells where periodic dimpled patterns are observed when the shell is constrained from within by a rigid mandrel. We find that the geometry of the system is central in setting the surface morphology. This prominence of geometry suggests a scalable, and tunable mechanism for reversible shape-morphing of spherical shells.