This is terrible advice. No diversification means feast or famine. Staying in cash means you are getting an (extremely) low return on your investment that doesn't even exceed the rate of inflation. You are essentially losing money daily if you have it in the average Checking/Saving account.
When Cuban said that diversification is for idiots, he was talking about people who think that they can make money by diversifying. If you're doing it to limit risk by putting eggs in many baskets then ok, I get it. But if you think this is a good way to make money then I'm sorry, you're a sucker.
If you let the money sit in savings and collect dust then yes, you will lose due to inflation. Have it in the bank until you can invest it into something you can have an edge in, such as your own business. You don't have an edge in the stock market.
And then invest it into things you can have an edge in (which excludes the stock market).
It's more about opportunity lost. Property may have risen 10%, stocks maybe 5%, and your bank cash is flat.
The amount of money doesn't change, you just get less for your money. $100 40 years ago could buy you more stuff than $100 can today.
