Debuggability and optimisation are traditionally regarded as in fundamental tension. This paper disputes that idea, arguing instead that both fully observable and fully optimised programs are possible. Although these two properties may not be achievable at the same time, it argues that metadata-based approaches extended with residual state can provide flexibility beyond that of dynamic deoptimisation. Correctness of debugging metadata is introduced as an ill-posed problem, a partial correctness criterion is proposed, and further approaches are discussed.