The study of unintended consequences is particularly significant when combined with the twin problem of optimization. Fuelled by the prospect that it will help us understand the workings of evolution and the principles of efficient design, optimization has been at the center of many recent studies on the network modeling of systems. In network optimization, surprising effects—some desirable, others undesirable—can be exacerbated due to interconnectivity and high dimensionality. In this talk, I will discuss implications of optimization for the metabolic network activity of living cells and its role in giving rise to the recently discovered phenomenon of synthetic rescues. Then I will discuss a fundamental but often overlooked question in the study of unintended consequences, namely, whether the intended actions themselves (not to say their consequences) are possible. For the latter, I will focus on control actions in the context of network controllability and show that theoretical results on optimizing the number of driver nodes often lead to control actions that are too complex to be implemented in practice.