I find the absence of a time machine to be one of the most vexing aspects of investing :)
But seriously, it doesn't matter what things were worth, only what they're worth today and their future expected risk adjusted returns. The investor psychology here is kind of fascinating. Eyeballing the S&P chart, we're back to around the same value as of 12/17/2020. If we had been trading flat since then would we be as bummed? If I think of the "money I've lost" with the market downturn, I'm really making a statement about an alternate world where I had sold all my stocks at the high. But I didn't. Basically none of us did, that's why it was at a high. In truth I never had those gains since I never captured them. So the line of reasoning only fills me with regret. And that regret is dangerous because it induces sunk cost bias.
I feel it too! Around December of last year I was thinking I should reduce my stock exposure, pay down debt, have more reserves. I knew that the market was crazy and felt overvalued. The problem is that I've felt that way at various points for the last five years and I know if I had done so five years ago I would've missed out on market gains; I'd be further behind than I am today. However, just as I didn't capture the gains at the high and so I was never "that rich", I've not captured the recent market loses so I'm also not "that poor" by comparison. Since I don't need to access my investments right now, at a practical level the only thing that's changed is some numbers in a spreadsheet and my anxiety level.
The way out of sunk cost bias is to say, each day, "Taxes and trading costs / commissions aside, if I was sitting on all cash today, what would I do?". That psychological trick helps to zero out mental time travel. Personally, I would probably end up with a portfolio about the same as what I have today. Each day as an investor we need to analyze what our best moves are.
Since I believe in the efficient market hypothesis and don't believe in market timing, my only move is to stick to my strategy. I may rebalance a little, the execution of which would look like selling some real estate to buy stocks. That thought scares me but that's what the math tells me I should do. I think it was Warren Buffet (or Albert Einstein or Mark Twain, all clever things seem to be attributed to one of those three) who said something along the lines of, "The stock market is the only market where buyers want to buy more when things are more expensive and avoid buying when things are on sale". We should do what we always should be doing: forget about the past and search for value.
All that aside, I do feel bad for those who are retired because withdrawing during a downmarket increases longevity risk due to sequence of returns. Hopefully they've constructed a balanced portfolio with reserves to wait it out.
As for the crypto bros, I'm less sympathetic since I always felt that the intrinsic value of crypto was $0.