It's always wise to diversify internationally as well as across different sectors of the economy. Volatile markets are only volatile in the short run. As you take a longer term perspective, volatility becomes less and less of an issue. When you have volatile markets you should just stay put, stick to it for the long run. Investors need to make a self-assessment of how much risk they can bear and you can bear a lot of risk if you keep your computer turned off and the news turned off when it starts talking about markets.
History is a good teacher because it's remarkably stable.
The average rate of return since 1926 has been about 11 percent for large firms and 13 percent for small firms. The average bear market is a decline of 25 percent, it only lasts an average of nine months and then quickly recovers an average of 36 percent.