This would have been terrible advice in 2017 when BTC broke past it's previous ATH of $1300.00. Not saying BTC is going to 10x from here, but a true warning from the past would be not to sell.
Because there's no upper limit to what someone will pay you for a random number backed by no assets.
You just described the entire financial system. Everything other than gold or a house falls into this category.
That is a false statement. For one thing, gold is not a productive asset; for another a house is not spectacular investment.
It would have been when it hit 10,000 and dropped below 5,000 for awhile. Depends on when you cash out.
The whole "you can't use the past to predict the future" thing goes both ways. It's pretty poor form to give unwarranted investment advice based on ignoring one of the few steadfast principles in finance.