Warren Buffett says this is the ‘biggest mistake’ people make with their money (and psst: it has to do with savings)

Warren Buffett, the infamous 91 year-old Oracle of Omaha, is worth roughly $100 billion — and could clearly spend frivolously. But Buffett is notorious for his spendthrift ways (remember, he eats at McDonald’s frequently) and his emphasis on creating financial security.  He’s also a big fan of learning to save money properly.