Everyone is saying the same and everyone have atleast tried it once by gambling to double their bitcoins but very few have made it true, as gambling is totally based on luck, it doesn't required any knowledge or skills, but yeah if you are lucky you can multiply your bitcoins by gambling and you can afford to take a risk once in a blue moon, if you win then you might have more then 4 BTC in your wallet depending upon the risk that you afford to take.