Holding is better than trading. If you buy Bitcoin, and hold it from 2017 to 2020 or 2020, you get profit.
If you buy Bitcoin in 2017 and trade it in 3 to 4 years to 2020 or 2021, I am not sure you will have profit now. If you use margin trading, I believe your orders would be liquidated many times in 3 or 4 years.
Don't take risk and practice margin trading. You will end with empty hands.
It is true that a great deal of the traders that tried to trade the markets during that time would have lost all their money, but at the end of the day each person needs to decide on their own what they are going to do with their money and if they want to trade despite the huge risks that this entails then they are within their rights to do so, I just hope that before people take the decision to become traders or not they really inform themselves about what they are against, as becoming a successful trader is one of the most difficult things we can do in this market.