Depending on your investment goals, a concentration strategy may help if you would take a higher risk to gain potentially higher returns, and a diversification strategy works better if your focus is lower risk. At the Daily Journal Corporation (DJCO) annual meeting on 16-Feb-2022, the 98-year-old Charlie Munger answered questions:

The Mungers have Berkshire stock, Costco stock, Chinese stocks through Li Lu, a little bit of Daily Journal stock, and a bunch of apartment houses. Do I think that’s perfect? No. Do I think it’s okay? Yes. I think the great lesson from the Mungers is you don’t need all this damn diversification and that’s plenty. You’re lucky if you’ve got four good assets.

I think the finance professors that sell the idea that perfect diversification is professional investment… If you’re trying to do better than average, you’re lucky if you have four things to buy. And to ask for 20 is really asking for egg in your beer. Very few people have enough brains to get 20 good investments.