Connect the two dots(two extreme conditions) and draw a curve, high chances are that at last, your profits from all investments may not be that much, at least much less than what you expected when you first gained that $10K. Therefore, all the occasional profits between investments may become fixed or variable costs that these investment must pay.
Does this sound logical to you ? What do you think of all the interval losses from the investment gains ? Please let me know.
You know that there are investors who bought bitcoin at a price of 1000 and still have not sold it, what do you think they would answer you? Your post is just a theoretical suggestion that you bought at the right time and sold at the right time, but it looks nice on paper, it's not in reality.
In addition, bitcoin shows that it can give more than just doubling your investment, it can be x4 or x5, and only in this case it is worth thinking about selling. There are different types of investors, some buy and wait for many years, others try to sell in a bull market to buy more bitcoins in a bear market, but in this case it is more like long-term trading.