How come he lost everything one day? Do most of the gamblers lose money in such way?
Can't say about most of the gamblers, but definitely not all of them lose everything they won. Here's a recent example of a guy winning big and spending a big part of it on useful things right away:
https://bitcointalksearch.org/topic/this-guy-gambles-and-wins-a-total-amount-of-400000-and-quits-while-ahead-5242283
I myself lost on many sites all my previous winnings there, but those were amounts from $20 to $50, the amounts I could afford to lose at the time, although not without bitter regret in some cases. But when I won $500 once($1.3k at the current BTC price), I immediately withdrew $470, leaving $30 on the site to play later(took me around a year to lose it eventually).
From my experience, it's pointless to say a guy who won big to withdraw all the money and never gamble again. What is more realistic is to withdraw 90% of it, and leave 10% to gamble with. Thus they will find themselves in win-win situation: if they won big again that would be great of course, but if they'd lose, they'd be happy about risking only 10% of their initial big win.