It's an investing rule of thumb: the greater return you seek, the greater your exposure to risk. Most of us know that a junk bond is more volatile than a savings bond. And we understand the difference between aggressive and conservative funds.

But in investing, risk comes in many shapes and sizes. Here are a few less obvious risks that some investors overlook.

The risk of not investing
The risk of playing it too safe
The risk of not planning ahead
The risk of extremes
The risk of solid investments