The difference is making smart decisions and making them sooner rather than later.

Let's consider two kids, Jason and Carl. Jason and Carl come from similar middle class families and they go to the same high school.

Jason is a keener. He is constantly studying and getting straight A's. He also does a number of extracurricular activities because he is aiming to get into an elite college and become an engineer one day.

Carl is not a keener. He goofs around, parties all the time, and doesn't really care that much about school. Carl typically gets B's and C's. He hasn't really thought too much about what he wants to do with his life.

Now let's see how their lives play out…

Jason, after a rigorous application process, ends up going to MIT for mechanical engineering. It's a very challenging program but Jason is up to the task. He buckles down and works harder than ever, and ends up getting an internship at NASA. During his final year in school, he goes through a gauntlet of job interviews and comes out with full-time job offers from the likes of NASA, Lockheed Martin, and Boeing. Jason takes the job at Boeing.

At Boeing, Jason finds himself at a company full of brilliant engineers. It's not easy to stand out but Jason does. Five years and two promotions later, Jason decides that it's time give his career a major boost, and he starts talking to Lockheed Martin again. Lockheed Martin is very impressed with what he's accomplished so far and they hire him into a senior role with a very generous salary increase.

Jason works hard and he's making very good money.

Carl, after applying to several colleges and programs, ends up going to a state college. A pretty good one, actually, but he majors in an area that doesn't have many career prospects. Carl continues his streak of academic mediocrity and doesn't do any internships. After graduation, he starts applying to several jobs. Some directly related to his degree, most of them not (they only require “a degree at some college”). After months of applying and interviewing, Carl takes a random job at a random company. The pay is okay and the work isn't bad.

After a few years, Carl notices that some of his friends are moving up the ranks in their careers. He sees them buying fancy new cars and traveling to exotic places. Carl wants that life. Carl wants more money. So Carl decides that he's going to start working harder than he's ever worked before. He busts his butt at work and his boss notices the change. After a few months, a supervisor role opens up and Carl gets offered the job. Carl is happy about the promotion but the pay increase is modest and nowhere near enough to afford a lifestyle of BMWs and trips to Positano. So Carl starts trying to find a new job. He interviews at several other companies but when it comes time to talk about salary, Carl is always disappointed. Carl is beginning to realize that no matter how hard he works, he isn't going to be moving up to a higher tax bracket any time soon. Still, he remains hopeful.

Carl works hard but he isn't making much money.

I know a “Carl.” He never took school seriously. He managed to find decent work but he didn't take his career seriously either until he got to his mid-late 20s. He looked at his successful friends and would say things like “I want to be a portfolio manager too! All you do is pick stocks, right? Can you get me a job there?”

The thing that Carl and many people like him fail to understand is that the success that they see in others is cumulative. They don't appreciate the amount of sacrifice and hard work that went on long before any success was within reach. Our friend Jason didn't just wake up one day in his 20s and decide “hey, wouldn't it be neat to work at a prestigious company and make a lot of money? I know what to do! I'll just take my complete lack of credentials to Lockheed Martin and they will surely make my dreams come true!” Jason got to where he is because he set himself on an ambitious and highly competitive path when he was barely a teenager.

Carl, on the other hand, unknowingly put himself on the same easy path as so many others that resulted in few if any in-demand skills. Carl can now work hard all he wants but at the end of the day, he's a dime a dozen. Carl is easily replaceable. Jason is not.

This is not to say that Carl should be punished for his poor decisions as a youngster. Because it's not about punishment or justice at all. It's simply the logical outcome of the market. You can't force a company to pay a dig ditcher a doctor-level salary simply because he works really hard. That doesn't make any sense.

Now I will of course say that there are exceptions to this. But the importance of making smart decisions as early as possible still stands. Consider how Asian cultures strongly value academics and emphasize a path not unlike Jason's. There is a reason why they have an extraordinary rate of upward economic mobility in America. They set themselves on the path to success at a very young age.