Some people may start investing in ETFs the same way they start buying stocks: they learn of an investment from a friend or an influencer or in an article they read, and then buy it without necessarily exploring the alternatives.Fortunately, ETFs, like stocks, are supremely liquid. If you don’t make the best selection at first, you can sell your holdings and replace them with more suitable ones in a matter of minutes.When it comes to core portfolio holdings—the basic building blocks of a por