For him, the glass that’s half empty/full isn’t either one or the other, but rather he sees the potential that it could actually become full. Overflowing, even, so that he would never be thirsty again.
Or perhaps he just wants to know what it’s like to win all the time; to be so right that even heaven can’t keep him out. (However, he prefers to think that he’s more addicted to the thrill of chasing a win, no matter how small a chance he has.)
So he casts the dice just one more time; throws the cards down and rakes in another part of the world until half (could be all!) of it is his, and for all his troubles, he never manages to feel complete ever again.