In situ nanomechanics is an emerging field that investigates the mechanical properties and deformation mechanisms of nanostructured materials. The study of in situ nanomechanics is often conducted by integrating the real-time mechanical testing inside an electron microscope and the mechanics modeling with atomic resolution. It provides a powerful approach to visualize the intrinsic nanomechanical behavior of materials - seeing is believing. In this talk, I will present recent in situ nanomechanics studies from my group, including deformation-induced stacking fault tetrahedra in FCC nanocrystals (Nature Communications, 4, 2340, 2013); fracture toughness of graphene (Nature Communications, 5, 3782, 2014); and twinning-dominated deformation in BCC nanowires (Nature Materials, 14, 594, 2015). The in situ nanomechanics studies provide new insights that cannot be offered by traditional mechanics studies. Ultimately, the in situ nanomechanics research aims to enable the design of nanostructured materials to realize their latent mechanical strength to the full.