But true that selling at $19k would have been better...
Taking an absolute view for or against is not the best choice. Selling at the timing of this thread would not given the best price, it had risen 300% from the previous peak but still was not near its highest price. The sensible thing is not to sell all but make sure your holdings are distributed some.
I dont especially agree with only hold but its not been a bad strategy for what is a unique new technology overall. Nobody was able to estimate it exactly and it was widely dismissed, holding was far from the worst strategy to have. Likely thats going to be repeated.
I would argue overall that people should adjust their portfolio to match gains seen. So if Bitcoin were to double in pricing then move at least some small percentage to long term currency like gold. Having your mortgage reduced so you are a larger percentage owner in your own house is a good arguable strategy for security. Money is security ultimately, some see it as luxury but having been poor many times in life I can tell you the most valuable money is what pays for food, security and all the basics taken for granted.
Always the best gains are stabilised across all your various costs, like rent, etc lopsided purely to growth, high risk products is dangerous ground