In January 2018, I didn't sell bitcoins for Tether (usdt) because I didn't believe in usdt. I thought the chances of Usdt being cheated are pretty high. I was wrong - usdt still exists.
Of course, it would be nice to sell Bitcoin for $ 19,000 and then buy for $ 3,500.
There was a bear market in 2018-2019. However, even then, it was possible to increase the number of bitcoins (by trading paired with altcoins). For example, in the spring of 2018, the price of the altcoin EOS reached $ 20 (which is an all-time high if we count its price in BTC). In 2018, Binance became the leading cryptocurrency exchange (previously Bitfinex and Bittrex were the leading exchanges). This circumstance led to the success of the BNB token.
The combination of the HODL strategy and speculation in altcoins has brought good profits.