My grandfather came over to America, worked in a box factory. At nights he took courses in accounting. When his kids were old enough he had them working part time jobs and they all pooled their money together. Eventually, they started investing in businesses where they could earn alternative forms of cash flow.
First it was bars/mechanic shops/restaurants, then it went into rental properties whenever real estate markets got very cheap (e.g.: he bought 10+ houses in Texas post-S&L crisis). This worked out pretty well.
Most of the successful immigrants I know did this. They came over, most were poor. They would sleep 4 to a 1 bedroom apartment. But eventually they found steady jobs, lived cheaply, and then invested the savings into a bunch of different things whenever the right opportunities came up. (The Patels in the motel biz are a good example of this).
The idea that your job/your one career should provide enough for you the rest of your life is just foolishly optimistic. You have to diversify to build in a margin of safety for when life throws a curve ball your way.