Planning laws promoting sustainable development have not stopped the depletion of natural capital and global life-support systems, fuelling arguments for degrowth and transitions to steady-state economies. To address this weakness, we employ scarcity multiplier theory (SMT) in a case study of Tasmania, Australia, where planning laws have the statutory objective of promoting sustainable development. By drawing on two seminal contributions of John Kenneth Galbraith, his squirrel wheel and problem of social balance, SMT explains how we fail to limit growth to match natural capital capacity. This application of SMT shows that new industrial developments in regions with circumstances similar to those of Tasmania produce two forms of unsustainability: ‘unsustainability of satisfactions of wants’ and ‘unsustainability of per capita abundance of natural capital’, the former producing an addiction to economic growth. We thereby argue that applications for approval of new industrial developments under Tasmania’s planning laws should be rejected unless these expansions are countered by a commensurate contraction elsewhere in that economy. In addition, we employ SMT to identify deficiencies in those planning laws that stop them producing sustainable development, demonstrating a need to reform government (and planning) to prevent such failure.