Mark Cuban has always had an entrepreneurial spirit, from selling stamps as a kid to cofounding Broadcast.com, which Yahoo bought for $5.7 billion. Along the way, he’s learned what really builds wealth — and one piece of advice he swears by goes against today’s startup norms. Be Aware: The$50 Mistake Warren Buffett Says Everyone Should Avoid Read Next: 6 Things You Must Do When Your Savings Reach $50,000 Here’s the unpopular advice he believes more entrepreneurs should follow to be wealthier in the long ...