As we climb the ladder of education, and especially in college, we think that the world is at our feet. When we graduate and get a job, we forget about these aspirations and instead start thinking very small (for example, replacing the goal of fighting world hunger with the goal of getting a car). And while in college we are naïve and overreach, later in life we underachieve.
Why we do that is still unclear to me; I think it has to do with a sense of complacency that being a grown-up brings with it; or us being hyperpragmatic since by the nature of most jobs they don't require us to think so we use our "mind cache" all the time.
Let's think big. The world is still at our feet. As my mentor said, we need to shift our thinking from "I want to do everything, but I can't do anything" to "I can do anything, but not everything I want". For most of our desires are reasonable and at least some are achievable within our lifetimes. We just need to start thinking.