The existence of risk is the "thing" that relates both trading and gambling to one another. But it seem to me that the similarity is more sided with gambling more than trading. Trading is like gambling because there is no assurance of profit because the market value is volatile and it would be hard to find a good trade, especially at this moment that the market value of cryptos are low, and no one knows when will uprise occur as well as which coin would go along with the uptrend. Gambling on the other hand is a bit like trading especially on strategical gambling games such as card game, a player would think of the best method in order to come up with the win. But as what I have said, it is risk which connects both gambling and trading to each other forming similarities.