Low ductility has long been the bottleneck especially at high strength in metallic structured materials due to conventional forest hardening having little to no effect. Hetero-structuring is an emerging strategy producing superior strength and ductility combination. This Viewpoint article delineates mechanisms for strain hardening and plastic deformation in gradient and lamellar structured materials. Both have typical trans-scale grain hierarchy, leading to sharp mechanical incompatibility and consequent strain gradient at hetero-interfaces during plastic deformation. This induces heterogeneous deformation-induced hardening, along with recovered forest hardening, jointly to improve ductility. The heterogeneous deformation-related deformation physics sheds lights on the path to designing novel heterostructures particularly for large ductility at high strength. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.