Fix your mind upon an unselfish goal in life. The moment you raise your mind from a selfish to an unselfish ideal you gain more energy to work. You no longer feel this mental fatigue. You can exert far greater power in your actions. Thus rising higher in your ideals, fix your mind upon the supreme Self within and work without ego or egocentric desires. Do not become mentally entangled in your work. Act in your homes, in your offices, in your society, with an impersonal attitude. Never become caught up with or attached to anything in the world. People believe that without attachment and involvement in worldly matters they will lack the motivation to work, to progress. This is not true. The truth is just the opposite. The very moment you become entangled in the world you diminish or even lose your capacity to work. You do not progress. Whereas, when you drop your egoism, dissolve your little self, when you are unattached, impersonal towards your work, then you turn out real work. This is karma yoga. Pursuing this path you will gain the supreme Self, the ultimate goal of human existence.
Bhagavad Gita by A. Parthasarathy