A lion is fully capable of capturing, killing, and eating a field mouse. But it turns out that the energy required to do so exceeds the caloric content of the mouse itself. So a lion that spent its day hunting and eating field mice would slowly starve to death. A lion can’t live on field mice. A lion needs antelope. Antelope are big animals. They take more speed and strength to capture and kill, and once killed, they provide a feast for the lion and her pride. A lion can live a long and happy life on a diet of antelope. The distinction is important. Are you spending all your time and exhausting all your energy catching field mice? In the short term it might give you a nice, rewarding feeling. But in the long run you’re going to die. So ask yourself at the end of the day, “Did I spend today chasing mice or hunting antelope?”
The above excerpt is taken from Tim Ferriss‘ 17 Questions That Changed My Life who had quoted Newt Gingrich, former Speaker of the U.S. House of Representatives using the above analogy.