Both the options have their own pros and cons as follows.
Investing in the stock market
As campare to start own business, investing in stocks, mutual funds or ETF’s take little time. We can invest money after consulting experts or doing market research and analysis. Losses are limited to the money you invest.
Investing conservatively and holding long term it is hard to not make money in stocks. Yes, people can lose money in the stock market. Usually for one of two reasons. They want to get rick quick and invest in risky areas such as day trading, options, Forex and the like or they panic when the market drops and chase high flying over priced stocks when the market is doing well.
Starting your own Business
I heard somewhere, 50% of all start up businesses fail within the first year and 75% of new businesses fail within 5 years. Most always the businesses fail because of shortage of money and lack of the ability to borrow money. Sometime the person who has started their business may have a large amount of debt that will take years to pay off.
People who wants to start their own business, they know all these things and still Owning a business is in high demand. People start their own business and worked 16–20 hours a day, 7 days a week for the first 3–4 years. If you want to run their own business and take it to long. You need to have a passion, You need to have a good understanding of marketing, finance, management, and lots more and you must be forever open-eyed and flexible.
The percentage of people who start their own business and become billionaires are most likely around .0001%. Those who become millionaires a probably in the range of 2%. It means, every businesses do not make you millionaire or billionaires. But no one knows, may be your business make you next billionaire. So keep working.
Many people do both. They own a business and also invest in stocks. There are people who have gotten rich both ways.