The rule is never to sell at a loss. Now the best strategy (if you really want to invest in the tech as well as have future financial independence) is to take some profits while leaving a core position for long term holding. For example, your coin goes up 3 times, cash out 1/3 or 2/3. A good goal or strategy is to be able to remove your entire Fiat investment while having a good number of digital assets or cryptos left in your portfolio for future gains. That way, when whales dump or market dips, you won't mind seeing your portfolio value drop by half or 30% or 70%, whatever the case may be, as you do not lose anything. The issue is some people invest for a quick buck, and when the market dips instead of rises, they are forced to sell, losing their investments.