Wrong moment, just like selling & buying. The best thing we can do it only to manage your cryptocurrency portfolio, set the percentage for the profit/stop loss.
Investment not always predicts the profit, but also you must predict how much percentage you can afford to lose. It's really hard for a common trader to face this kind of situation, also i meet this situation several times.
We cannot predict it. The other day, I found an article (which was written in 2016 only, not long ago!). there, the so-called crypto expert writes that he is sure that in several years, Bitcoin "can reach 10 thousand dollars". However, in a year (I mean after the publication) BTC jumped to 20 thousand. Therefore, these predictions do not mean much.