But again, most of those that earn less do not do so simply because they are unwilling or less ambitious.
That may or may not be true, but sometimes life becomes perilously difficult despite hard work. My father joined the Army after high school, worked his way through college (holding down three jobs and a full load of courses), re-joined the Army as an officer, and sought a graduate degree in computer science after becoming a civilian again, using the G.I. Bill to pay for school and working as a lab instructor to feed our family. This was a decade or so before the dot com boom. Had everything continued to go right, he would've almost certainly have become as wealthy as did his peers.
But it didn't go right. One of my siblings became sick and almost died. My father couldn't afford health insurance as a student teacher, and the medical expenses nearly bankrupted our family. My father had to leave school, and spent the next decade trying to make enough money in poorly paying jobs to get by. I didn't know it at the time, but we almost didn't eat some days. Some days my parents didn't. Some nights, they went to sleep not knowing how they were going to feed their kids the next day.
Eventually, we made it out through the Army. My mother went to school once we were old enough to look after ourselves for part of the day, and she returned to active duty as an officer (my parents met as officers in the Army). By the start of my junior year of college, they finally paid off the medical bills from my sibling's illness when I was three. (He died, medical efforts not withstanding.)
All of this - all of this poverty, this worry, this starving, this struggle - because we lived in a country without universal health care. My parents are some of the hardest-working persons I know of. My father worked sixteen hour days, every day, for months at a time. My mother gets to her office at 0700 every day, and usually doesn't leave for home until 2000 at night. They work hard.
And they couldn't make it - couldn't keep their children out of poverty - in a country that's supposed to offer nothing but opportunity. Opportunity for those who work hard, who think cleverly, who act with ambition. But apparently not for those whose children get sick.