I really don't understand the difficulty in buy-holding index fund (not stocks, that can be wiped out. Index fund is more difficult)
Share do not represent your money. They are not a checking account. Sometimes in the past you made a choice: buy some shares of the 500 most successful companies in the USA (S&P 500 example).
The instantaneous value has absolutely no meaning. You lose money only when you sell at loss. If you don't sell, the shares are not money: they are pieces of businesses that try to emerge from a bear market .
During a crash, I'm honestly horrified at the thought of selling at loss, not on keeping share of companies which instantaneous value is falling. The idea of selling at loss, independent from the causes, I personally find it quite upsetting.
The same is true for your home: nobody really looks continously at the price of their home or let them appreciate every 10 seconds. And if something happens in your neighbouroud, some kind of heavy construction works that will be going on for 3-5 years, halving your home value in the mean time, you will probably not sell and go away but just tough it out and wait for those years to pass. That's because you don't mistake home for money, you don't do the equation home = checking account.
But I have this impression that this thing to always have the instantaneous price of your portfolio mislead many people in thinking that losses or gains are real (which are not, until you sell) and your shares are some sort of checking account.