@NoraLenderbee @Terrestrial
Think of this as a loss minimization strategy. Of course, when the market is good like right now, you are not going to use it.
But if the WHOLE market (not just specific sectors) does drop in a steady fashion over several weeks, pretty reasonable to say its a financial crash rather than a nuisance pullback. Why 15-20%? Because smaller percentage would include volatility and pullbacks.
Why not 30, 40% 50%, etc? Because You can't predict the bottom ( see below) and it might be already too late.
How do you know when it bottomed out? You can't. You just wait (at least 3+ months) and see if the whole market is rising in a CONSISTENT fashion. (Take weekly prices or SMA50/200 to see the larger trend.)
There are so many things wrong with these broad generalizations/assumptions about percentages and time frames of market movement that I'm not going to tackle them. Since you seem pretty set in your ways I really hope you try this to 'minimize your losses'.
This is what I will say. You are dead wrong that this is a 'loss minimization strategy'. What you advocate is a
loss guarantee strategy. Let me explain. By selling at 15% down you guarantee that you are selling at 15% less (this may or may not be 'losses' depending on your basis, but the point remains) and are locking that in. Perhaps you will time it well enough to buy back lower and it works out. Many credible studies have postulated that you won't, at least not consistently.
Let's be clear, paper losses are not losses. They are an adjustment to current value of an asset. If you don't sell it you haven't lost anything. If you HAVE to sell it you were probably investing money you shouldn't have so sucks for you and better luck next time.
You know who didn't lose anything in the financial collapse? Me...and probably a lot of other people on this forum, who left our accounts alone and now have a minimum of 35% more money than in 2007 by not doing stupid stuff. For those smart enough to leave their accounts alone and also buy regularly on the way down and back up that return is substantially more.
Warren Buffett and countless other
professional,
successful investors have written extensively about how this type of scheme is total poppycock, fyi. As a quick anecdote, Buffett's preferred holding period is a one word answer,
forever, not 'until the market goes down 15% which probably means it's not just a nuisance pullback but a major crash so sell because the financial system is collapsing but be sure to buy again after the market is stable for 3 months and hopefully that's lower than where you sold but maybe not.'