Many people think that education, ability, or luck determine the gap in social class.

Wrong, it's the means of production.
There is an old post on Tianya that explains it thoroughly: when you're young, you can work like a donkey to earn money, but if the hard-earned savings are just deposits and not means of continuous productive output, then you are a "rich donkey." When you're old and weak, you'll be out of commission immediately.
The key is to buy the right "mill." It doesn't have to be high-growth, but it must be able to produce steadily for ten or eight years.
Even with limited savings, there are ways. Use professional skills to create courses, build systems—selling to one person is selling, selling to a hundred people is also selling—that's the means of production. If you're lucky, a reliable equity investment can also work.
In short, don't just "work day by day" like a donkey. Save when you're young, and invest your money and energy into assets that can generate compound interest.
Most of the worries in this world are the worries of "donkeys." Only by not being a donkey will your worries decrease.