Annuities are insurance contracts which establish regular payments to an individual by the insurance company, typically lasting until said individual's end of life.
Usually, the individual gives the company a large cash sum, and in return receives these payments subsequently. Annuities are made feasible by returns from investing that initial cash sum.
Obviously this works very well to the insurance company's benefit as long as investment profits are high. However, what will happen in a long bear market?
The companies providing the annuities will end up losing money on all their existing annuity obligations. This seems especially risky since they may go out of business, leaving their insured without income or capital to support themselves in retirement.