Sodium has been recently attracted considerable attention as a promising charge carrier, but this sudden attention has made the strategy of research somewhat hazy, as most research reports are indeed the examination of typical materials rather than following a solid roadmap for developing practical cells. Although the history of sodium-ion batteries (NIBs) is as old as that of lithium-ion batteries (LIBs), the potential of NIB had been neglected for decades until recently. Most of the current electrode materials of NIBs have been previously examined in LIBs. Therefore, a better connection of these two sister energy storage systems can shed light on the possibilities for the pragmatic design of NIBs. The first step is to realise the fundamental differences between the kinetics and thermodynamics of Na as compared with those of Li. In fact, tiny differences between the electrochemical behaviours of these systems can lead us to new practical ideas for designing suitable materials. Furthermore, NIBs should be considered as new opportunities for energy storage rather than replacing LIBs. Hence, the subtle strategy of research is to learn from LIBs but not replicate them when designing NIBs.