I am a believer of working for something greater than yourself. Best motivation is figuring out what gives meaning to your life, and doing your job to get closer to your purpose.
I have not seen anyone who can motivate himself continuously for his own gain. Everyone who inspired me to act either acted or believed that they are fulfilling their life's purpose, the reason why they exist. No one has inspired me by telling me how early I can retire by working extra hours.
I believe that's because we all want to be a part of something greater. We all want to belong to something. We need to share purpose with people around us.
Simon Sinek shared his view of how great leaders inspire. They inspire us by describing the purpose. Great leaders don't start with what we should do or how we should do things, but rather why we should. They help us see the bigger meaning of why we must. They communicate the shared value for the rest of us to emulate.