There is already risk on it when you invested in Bitcoin but it is minimal only. Now the price of it went down below the price you bought it and choose to gamble your Bitcoin, that adds more risk on it and that is called "GREEDINESS". As an investor, you must stay calm and ready in times like this.

If I will put myself in the situation as same as John, I'd rather accumulate more Bitcoin at a lower price (average down) rather than gambling it. In that case, the risk is lesser than putting it in an investment where the risk is at its highest (gambling). We know already that most gamblers end up losing on gambling so why would you risk it if you can think of a better way.

Lucky for me that I didn't experienced this at this moment but for some investors who bought their Bitcoin at early 2018, probably they gamble their Bitcoin just to increase their Bitcoin holdings.