Being healthy is simple, right? "Eat less, move more." That's easy to say, but practicality is one of the most important things when it comes to health and fitness. Recommendations like this are blanket statements that don't address practicality—so when it comes down to it, which is more important? Diet, or exercise?
Yes, we should all eat healthier. Yes, we should exercise every day. There are infinite things we could do in order to be healthier, like sit less, eat more vegetables, eat less processed food, or drink less alcohol. But they don't take into account the reality of life: we are all constrained by a finite amount of resources such as time, energy, willpower, and money. Recommendations that don't take this into account can easily make us feel like we are failing our fitness and health goals.
To give you a sense of the importance of practicality, consider this recent meta-study (i.e. a study of studies), published in the Journal of the American Medical Association, which sought to figure out "which diet works best?" by looking at the results of 59 individual studies. These studies included various nutritional recommendations, such as low-fat, low-carb, and so on. Which of these recommendations reigned king? None. There were no major differences between the diets, and success was completely dependent on what the individual could adhere to. In other words, practicality reigned king.