Honestly, this is one of the best advice I've ever received in terms of cryptocurrency investment, because when I sat down and thought about it, I realized it's a lot like gambling, but with a few differences: in cryptocurrency trading, if you don't sell, you're not a complete loser, whereas in gambling, if your predictions are wrong, you lose everything. So, in my opinion, it is still a good idea to invest the amount that one cannot afford to lose, in order to keep focused even if the market is down and wait for the proper time, rather than panic and sell at a loss.