Our job as hydrologists is to understand and predict the water cycle. Historically, prediction of river flow has been at the centre of our attention. This is not surprising: rivers form a crucial resource, shape our environment, cause natural hazards, and are "easy" to observe. In future, study of river flow will obviously remain important. However, in this blog post we argue that shifting focus towards another part of the hydrological cycle can provide significant opportunities. Inspired by the 'meet the expert in hydrology -- the mystery of evaporation' session held at the 2015 EGU General Assembly in Vienna, we discuss the role of evaporation in hydrological research and how evaporation affects our ability to understand the water cycle (including river flow predictions!). We do this by exploring (a simplified view on) what we know about evaporation, what key limitations exist in evaporation research, and what the implications are for how we currently do our science. To conclude we provide suggestions on how to better consider evaporation in hydrological research.