I have about a 70/30 portfolio between stocks and fixed income. In a downturn, I would sell some bonds, to rebalance, and then perhaps, add 2% more of my portfolio for every 10% drop. So after a 10% drop, I would have a 72/28 portfolio.

That's not going to have much effect. An additional 2% in stocks is not enough to make a significant difference.

Also, you didn't say anything about a plan to move money back out of stocks into bonds. Your plan has to account for _all_ movement of money----which is where a number of my tentative plans have foundered.

********************************************************
In a downturn, I would sell some bonds, to rebalance, and then perhaps, add 2% more of my portfolio for every 10% drop.

Well, did you?

From 2/10/2020 to 3/16/2020 the S&P500 dropped -30%. That's 3 10% drops.

From 12/27/2021 the S&P500 dropped -11% on 3/7/2022, then went up a bit then dropped to -22% on 6/8/2022. That's 2 10% drops.

It is a lot harder to actually execute your planned strategy than to create it.

William Bernstein:
Successful investors need the emotional discipline to execute their planned strategy faithfully, 
come hell, high water, or the apparent end of capitalism as we know it. 
' Stay the course ' : It sounds so easy when uttered at high tide. Unfortunately, when the water 
recedes, it is not.

Wall Street is littered with the bones of those who knew just what to do, but could not 
bring themselves to do it.

abnormalreturns.com:
The challenge is not for most investors in coming up with a workable investment strategy, 
but in trying to implement that strategy on an ongoing basis. The problem arises that there 
is always a plausible reason NOT to do something our strategy is telling us to do. 
The smarter someone is the more plausible a story they can come up with telling them their system is incorrect.

---------
This thread really belongs on the MI board, where you cross-posted it, not the BRK board.