Whenever you are tired, learn to rest never quit. This is the basic principle of self motivation for more achievements.
Desires for more progress requires motivation. Sometimes I sit down get a journal, do a life audit and propose means to be better. This is a form of self motivation.
Avoiding fear of taking positive steps is a virtue that can motivate more productivity.
Paying the price and sacrifices of sharpening one's skills and securing intellectual relationships with people is another effective motivation.
So, What keeps you moving can be seen as a sense of motivation ranging from intellectual people around you, financial rewards, passion and self drive, but for me what keeps me moving is self drive and passion. Before I go on with any journey, I make sure it's something I have passion for first and I believe it's a futuristic investment. Apart from people's intellectual influences or rewards motivation, I'm often self motivated for anything I have passion for and this help me grow gradually.
Many are challenged by others for competitive reasons only, rather than the motive to improve and be better.
So! apart from being challenged by other successful people, you have to be your greatest competition and motivator.
For me, i want to do my best to contribute positively in my world. I always tell myself within that I'm not the best of me yet even when people applaude me.. I appreciate and criticize myself personally, i always think of the potentials within me to do better.
I improve myself not to compete with others but to drive myself to the best version of me and increase my self value daily.
Being self motivated in addition to other people's intellectual inspiration to you will mitigate the possibilities of giving up easily on desired next level. However! It's a gradual process. Never quit from within!!