In fact, this is a fundamental question. Knowing the correct answer to which almost becomes any trader a wealthy person. But the joke is that there is no answer to it. It is impossible to guess the perfect time for a sale. And even if you succeeded and you sold at the very peak of the price, this does not at all guarantee that you will be able to buy again at the very bottom. Otherwise, you would be a genius of the trading.
All are mostly speculations, even you are following certain patterns it's not a guarantee that things will go according to how you percept the market.
And likewise, there are no perfect strategy that will keeps you in a winning position, timing is always important just need to be patient in order to have a much higher chance of getting profits.
It's always up to every traders on when they plan to sell, some are good while others are greed.
You have to plan and always keep yourself updated to avoid busting your investment.