1. The social security system can make up for the huge gap in market income distribution and is an important tool for government income redistribution.

2. Under the condition of market economy, the social security system has the function of "internal stabilizer"

3. The government can undertake the social security responsibility that the private insurance market can't fully fulfill.

① Adverse selection and moral hazard exist in the private insurance market, which will lead to the failure of the private insurance market.

② Private insurance can't solve the problems of insufficient personal savings and "hitchhiking".

③ The private insurance market is hard to resist systemic risks.

④ Private insurance market can't redistribute income purposefully.