Predictability is examined in plant responsiveness to stress, along with extents of resource trade-offs in growth/defence allocation, value of conflicting findings for theory development, and eventually, need for new theoretical concepts on the book’s subject. “Opportunities” are summarized plants possess in regulating resource allocation beyond apparent trade-offs and their associated “opportunity costs”, mediating to empirical and theoretical means for enhancing predictability. Acknowledging high functional and structural plasticity, and hence complexity, in plant responsiveness as a key feature of evolutionary success, both empirical capacities of molecular research are summarized in strengthening predictability across spatio-temporal scales and modelling as interacting theoretical concepts. Novel numerical and statistical modelling approaches are comprehended in reconciling conflicting empirical evidence and assessing degrees of universality. Not being unifying renders the “growth–differentiation-balance theory” falsifiable towards mechanistic consolidation as the grounds of advanced theory building. Mechanistic comprehension of plasticity becomes the key to plant system understanding.