For many in America, housing remains the only investment they've made that has worked without fail.

And real estate is not the only risky investment on the life insurance side.

Life insurance could be the only investment they can afford to maintain.

Charity and personal force are the only investments worth any thing.

If baby boomers concerned about retirement continue to believe the stock market is the only possible investment.

"Your only investment will be the paper and the ink."

What's more, he said, "it could also work for a lot of individuals as their only investment."

This is the only significant financial investment that has two functions.

But, she said, "you wouldn't want to make that your only investment," for several reasons.

"But I always say that the only investment that's kept pace with higher education is the stock market."