Yes, this is indeed your fatal mistake. You should not buy all the coins you hold at a high price. Because this is certainly very risky. If the coin you hold can rise higher again it does not matter. The problem is if you buy at a high price then the coin drops drastically and you instead sell it at a low price. Surely you are losing a lot of money from your investment returns. But all the events that happen to you should be made as a lesson and experience are very valuable so that the future does not repeat the same incident.