Generally people lack self control and that is the reason they end up loosing as if they win at initial stage then it will make them greedy and will start thinking that they can win more but it doesn't happen every time and if they loose they gamble even more to recover their money, gambling is only good if you know your limits and when to quit.
e.g. that he make a profit double with the amount of 0.01 btc and make 0.01 profit so he has 0.02btc now because of greediness and not satisfied what he win he gamble it again and bet all in. the result are lose this most of the result in the end.. but if you can be satisfied you can gain that profuit.. many people are not satisfied with small amount they want to make larger profit everytime they are gamble because they are targeting to make a large profit.. unlike rich people that they are just gamble for fun..