Money Magazine and other financial publications have a variety of "model portfolios" that cover a range of risk tolerances ranging from aggressive investor to very important to preserve investment, such as might befit a person with only a short time-horizon of investment. From my prior experience, market volatility only creates major deviations from a long-term upward trend for periods of a year or two - though certainly there have been longer market downturns prior to my time in the market. I think most of the money I invest is still going to be in the market in 15 years, so although I am retired I consider myself to be a fairly long term investor. But I cannot quite stomach the wild gyrations that a truly aggressive portfolio would entail. So I have not sought the high returns of REITs, junk bonds, emerging markets, or various specialty industry funds. These types of investments can lead to higher returns as befits their higher risk. But neither do I grasp my investment compulsively - money market fund returns are so low as to be of no interest, IMHO. But it is a very subjective matter. It depends on individual disposition, investment horizon, living circumstances and personal flexibility to deal with loss. There can only be guidance but no "correct" solution.