We have to get back anything we lost in gambling means we must invest some more money and win our bet or else it is not possible.
When you lose money in trading i am pretty sure you need to invest more money if you want to return money. As long as we don't sell our coins and keep holding it, there's still a possibility for us to get profit. What we have to do is just to be patient. To make another investments aren't necessary in such cases. The bad habit that some people have is, they got panicked when the price move against them.
If you know that the coin you invested got a good future then you no need to worry about for short-term price fluctuation. But if you got some extra funds then you can take this opportunity to buy some more to average down your buy price. If you have invested money without the coin knowledge then you may be a panic when prices go down and sell it at losses so don't invest money without understanding the product.
I was once a heavy gambler and fortunejack, primedice, and bitsler people can attest to that because I've lost a couple of whole bitcoins playing there. I guess more than 3 bitcoins in FJ, 2 bitcoins in primedice, and 1 bitcoin in bitsler (not to mention other sites 