Nobody should be planning on steady stock market gains for their retirement income. The stock market goes up and it goes down. In both the dot com crash and the 2008 financial crisis the market fell significantly more. Even in Covid it fell more. So you should plan for many of these events to happen within your retirement. If you're more conservative (pun?) you should plan for great depression style events within your retirement.

EDIT: I don't usually respond to downvotes but it's really important to understand the stock market is a volatile investment. You shouldn't have money you're planning to use in the short or medium term in the stock market. It's a longer term (10 years+) investment.