Traditionally, risk was considered related to leverage. A company that borrows to fund 80% of its assets is more risky than its twin that only borrows 20%. This is because leverage amplifies both positive and negative returns. If information suggests both companies will earn $1M more profit this year, the shares of the leveraged company will rise more than the un-leveraged company because in the leveraged company there are fewer shares to distribute the profits among. However, news suggesting both companies would earn $1M less would more adversely affect the leveraged company. Thus, as good and bad news swishes around, both companies' shares rise and fall, but the levered company would be much more variable - and thus its beta would be higher. Beta would be telling you "this company will probably go up or down faster than the market."
Beta was also traditionally thought of as a combo of systemic (market) risk and unsystematic (asset-specific) risk. You can pick a great company with low unsystematic risk, but if it's early 2008, the market risk is about to wipe you out anyway. Similarly, you could have bought Sears during this bull market, but the unsystematic risk of that company would have wiped out your investment despite the market. These outcomes might make it look like beta didn't matter, but beta is not for predicting outcomes, it's a ratio of covariance to the market.
This matters for the financially independent because, yes, you are forced to sell at bottoms! For example, if you went into 2008 with an all-stock portfolio and you were living off the proceeds, you would be forced to sell all the way down to cover living expenses each month, week, or whatever. Instead of selling 10 shares of X to keep the electricity on, you'd have to sell 20 (dividends were often cut or suspended, BTW). Those lowball sells would have decimated the future value of your portfolio, and caused you to miss much of the rebound. It's dollar-cost-averaging in reverse.
If your portfolio was high-beta, it would have been even worse because the shares you had to sell would fall further than low-beta shares, forcing you to sell more of them than if you had bought the low-beta shares. Maybe instead of selling 10 shares of Y, you have to sell 30. The shares may completely recover, but you won't.
For those aspiring to FIRE, this matters because we have to decide if we want to risk a recession or correction adding years of hard labor to our lives. Yes, the expected return of those high-beta stocks/portfolios is higher (see Capital Assets Pricing Model), which means we could plausibly escape cubicle jail a couple years earlier by embracing more risk. However, if the market takes a poo, we might have to work several more years thanks to our decision to go high-beta. It's like the prisoner's dilemma.
Beta is about the only quantitative metric for risk, so I am reluctant to toss it out in favor of ...what? ...opinions? ...intuition? ...smell? However, we should keep in mind beta is an objective measure of other investors' behavior. It assumes they rationally and consistently respond to the news. I'm not sure if that's true across time. Investors' sensitivity to things like rising interest rates, political instability, or widespread bankruptcies seem to change over time. These days, investors say "meh", but in other time periods, these news items might have justified a correction.
Just don't make the mistake of comparing beta across asset classes. A stock and its put option are not comparable in beta terms. One goes up and the other goes down and vice versa. Stocks and bonds are sometimes correlated, sometimes not. Also, don't make the mistake of thinking a portfolio of high-beta stocks averages out to the risk of a low-beta stock. They're correlated assets.
This time is not different, and the best you can do is (a) reduce unsystematic risk through diversification, and (b) select a level of risk / leverage / beta that you can live with through a large downturn. That's 55 year old advice, but don't be fooled into thinking something fundamental has changed.