I've come to embrace the notion that I haven't done enough in my life. I've come to confirm that one's title, even a title like president of the United States, says very little about how well one's life has been led. No matter how much you've done or how successful you've been, there's always more to do, always more to learn, and always more to achieve.
There is no success without sacrifice. If you succeed without sacrifice it is because someone has suffered before you. If you sacrifice without success it is because someone will succeed after.
The key to realizing a dream is to focus not on success but significance - and then even the small steps and little victories along your path will take on greater meaning.