If you can earn $150k a year, and your living expenses are $30k and you have no kids, you can squirrel away cash pretty fast.
Tesla is certainly a risk, but it's one of the few companies that actually has a plan which would lead to a trillion dollar market cap if successful. It's not insane to put the bulk of your net worth in an investment like that if you only care about potential upside, not the downside.
My salary is less than that, and I'm married with a kid, but I earn about as much from side projects as my salary, so it makes for quick saving (after taxes)
I own 3,000 Tesla shares. Purchased most shares at $30 after driving my model s from the factory. I have seen my net worth get cut in half when tsla went from $280 to $140, but never sold any.
LinkedIn, a crappy website, was recently purchased by Microsoft for $30 billion. That's about how much Tesla's market capitalization was 2 months ago.
Take a look at the all of the industries that will be impacted by the convergence of self driving cars, electric cars, and ride sharing.
The global parking industry alone, is a $100 billion dollar industry. Other impacted industries include oil, traditional auto, car insurance, auto repair/servicing/maintenance, auto dealers, etc.
Batteries are getting cheaper than anyone ever expected at this point. Solar recently became more competitive for electricity generation than fossil fuels.