Know that whatever you will become is a function of your thoughts. We are what we think. With our thoughts we make our world. What you picture in your mind, your mind will accomplish for you.
Consider the image above. While the world saw a cat, the cat saw himself a Lion! We could be greater if we can guide/guard our thoughts.
Resist low thinking, self pity, self comparison and depression. Be positive. Equate thoughts of failure with success, miserliness with wealthiness, pain with joy, hopelessness with hope, strife with peace and hate with love. Be determined to control your thoughts.
Think big and achieve big!