As others point out, buying at rich valuation levels has a huge impact on forward returns...

Indeed. Even having a very rough idea of where the value sits is a lot better than no idea. So, a rough idea:

FWIW, I have found Alphabet's price to sales ratio worth watching as a quick gauge, as their margins are somewhat variable. The "fair" P/S ratio should definitely glide down over time, but in recent years entry prices under 6 have generally worked out pretty well in a reasonable time frame. (e.g., if cyclically adjusted net margins are 20-25%, P/S of 6 is 24-30 times trailing earnings. If they manage 20%/year EPS growth for three more years, it's a P/forward-forward-forward-E of 13.9 to 17.4)

The current P/S figure of around 5.83 is not nearly as attractive as the lows in the 4-5 range in the winter of 2022-2023.

But it's about the same P/S as in March 2020, which worked out very well. Also similar to May-August 2022 which worked out well but only if you held over a year. And pretty similar to its range 6-12 months ago, which worked out well as long as you held only until the peak around July, OR you're still holding till whenever the next high price comes around.

I added to my relatively small long term position recently, and plan to add more on the way down. I don't expect a huge price rebound any time soon this time. The legal challenges are likely to have a long and winding road for years--keeping prices perhaps somewhat depressed on average and perhaps news-reactive for a while. But as long as the underlying business is printing money, of which I have no doubt, good outcomes will arrive at some point.

Jim