Traditional life insurance protects investors if they die unexpectedly, but an annuity protects investors who live a long time. Your annuity-invested funds are available as a series of periodic payments that are guaranteed as to amount and schedule. If you choose to take annuity payments over your life time (there are many other options), you have a guaranteed source of income until your death.
Here's the breakdown:

• If you don't outlive your life expectancy, your beneficiaries may receive less than you paid in.
• If you outlive your life expectancy, you may get back far more than you paid in.

By comparison, putting your funds in a traditional investment means you may run out of funds before your death. Often, investors choose to augment their more traditional retirement investments with an annuity as extra assurance and a guarantee if the traditional investments run out.