Nice Guys tend to have a deprivation mindset. This way of thinking started early in his development because the Nice Guy's needs were not met in a timely and generous way. As a child, the Nice Guy concluded that there "isn't enough for him," and developed a fear that his needs would always go unmet. The Nice Guy developed a core belief that the world is a place of lack rather than abundance.
The Nice Guy's belief that "there isn't enough," eventually morphs into an idea that "I am not enough." As a result, the Nice Guy withholds showing up in the world with the fullness of his strength. The Nice Guy is only moderately successful, never risking it all or going all in because he has been conditioned to believe that he doesn't have what it takes to be truly outstanding.
Then integrated man sees the world as a place of abundance. He believes there is "more than enough" for everyone. The belief of abundance frees him up to live from his heart, give his love, and offer his strength to the world. The integrated man isn't afraid to love, to show compassion, and to give because he knows there is an infinite resource in which to draw available to him at all times.
When we "think abundance," we begin to shift away from selfishness into freely giving of all our resources. When we freely give, we replenished with the infinite abundance of the universe has to offer.