A lot of financial advice gets complicated fast. Charts, timing the market, chasing the next big thing. "Shark Tank" investor Kevin O'Leary thinks a 20-year-old with just $1,000 can skip all of that. In a YouTube Short, O'Leary laid out what he believes is one of the simplest paths to building long-term wealth. "What's the smartest thing a 20-year-old can do with $1,000? This is so simple," O'Leary said. "Put it into the stock index and forget about it for the rest of your life until you retire.