But if you lose 30% of 100k then make back 30% your still down 10k or so
That's only if you purchased all of your shares at $100.
Let's round up UPS stock to $100 because math. So at $100k, you currently have 1000 shares. A 30% drop and bounce back shouldn't necessarily leave you at $91k because the investment strategy that got you to 1000 shares will also allow you to accumulate more shares at $70.
Not to mention that you most certainly purchased most of your shares well below $100 as it is. I mean, if you started 5 years ago, you bought UPS at $60.