Imagine that you own a business that is gigantic and yet, year after year, revenues grow by 15-20% a year.
Also, your profit margin is close to 30% (which means that every time you make a 1$ sale, you get 30 cents of profit). For a lot of people, including myself not so long ago, profit margins didn't really impress me. But after an analysis of a lot of stocks, I know that profit margins over 20% is exceptional.
Also, your products have almost no competition. Facebook/Instagram is the only dominant social media in the world. Windows/Office is the only dominant software/exploitation system for computers in the world.
Also, your ROE is over 20.
Also, you have a small debt, or almost no debt.
Also, nothing shows that your products will face some serious challenges in the near future.
Finally, you've got enough money to buy any company which would represent a threat for you. Actually, you've got more money than a lot of countries.
Everything written above could be applied to Facebook and Microsoft. It could also be applied, to some extent, to Google, Apple and Amazon.
These businesses are the biggest in the world, yet they outperform at least 90% of the stocks out there. Yes, they are expensive, but their valuation is still rational because they make a lot of money. Tons of money actually ( revenues for the last quarter: 43 billion dollars for Microsoft and 28 billion dollars for Facebook).
In 2021, that's the best sector to invest money. Perhaps it won't be the case forever. Perhaps the next big thing will be retail stores like Bed Bath and Beyond and Sears, but right now, I don't see any sector better than that.