Not every rich people made returns from their every investments, I read somewhere the best ever and most successful investor of all time who is Warren Buffett even have the success rate of 6 or 7 out of 10 means you can still lose no matter how good your investment plan is. Never borrow money to invest, just make money and start investing. Life is simple but don't complicate it with things which you can't actually control.
Another thing is to learn to diversify our investment. Diversification is very important but a lot of people never knows that. Like you said : Warren Buffet has the success rate of 6 or 7 out of 10, showing that he doesn’t just invest his money in one, but different assets. Imagine he invested only in one, and that one investment happens to be the one that is not successful, what will he do?
Another very important thing that we need to learn is how to know the right projects to invest in. You have to be able to tell the good ones that are more likely to succeed in the market, if not, it’s going to be a waste of time diversifying. I have seen people who invested in different assets and at the end of the day 90% of their portfolio was a loss.