Moody's downgrade of the U.S. credit rating to AA1 from AAA sent shockwaves through the market, but Thierry Wizman says investors should keep things in perspective. Wizman notes that while the downgrade is a "yellow flag" for the U.S. economy, it's not a default event. Instead, he believes it highlights the country's long-term fiscal issues, including its growing debt-to-GDP ratio and the unpredictability of U.S. policy making.