Tyresian

Over at Bogelheads they always like to post articles like this (time in the market is better than timing the market) which should make you feel better.

https://www.personalfinanceclub.com/how-to-perfectly-time-th...

What makes you think bonds are stable? Vanguard's Total Bond Market Fund is down 8.03% in the past 3 months / 10.54% in the past year.

In regards to risk adjustment you can change your investments / asset allocation.

Target Date Funds do this automatically, otherwise you can manually move the investments. You'd only want to do this in retirement accounts or else you'll pay taxes on moving the money though.

If you mean buying actual bonds, that is a good method to mitigate risk, but most people can't do that in a retirement account.