The second longest bull market in history has lulled Main Street into complacency. U.S. investors expect their portfolios to generate an 8.5 percent return annually over the long term after inflation. Financial advisors said a 5.9 percent return is more reasonable, according to new research by Natixis Global Asset Management. The mismatched expectations could mean investors are saving less than they should to reach their retirement goals. And it appears to be a global problem. Individual investors, on average, said they would need to earn an annual return of 8.5 percent above inflation to achieve their investment goals. And 70 percent of those investors said they can realistically reach that level of return over the long term. Millennials are even more optimistic, with investors between the ages of 18 and 34 expecting...