Usually everyone agrees that in gambling everything depends on luck (and not on your mood or skills), and the advantage is on the side of the casino. Thus, in the "normal/average" variant, the player gradually loses money and does not consistently earn it (which is generally a rarer case than even the jackpot). Thus, it is quite expected to be surprised that someone plans to spend (and seems to really spend) the money that he earns on gambling.
I reckon in most cases of planning in advance in winnings, it's only a part of the profit that's realized. Like 1/4 of the entire bankroll would be considered and then calculate depending on the games they play. It might also even be an average in terms of their monthly winnings, which is probably not reliable, but hey, it's a reasonable measure.
This is hardly a reasonable measure. Let's say he plays with low odds - this means that he can count on profits with great confidence, but sometimes he will lose a huge (compared to winnings) amount. Or vice versa, he plays with large odds - this means a huge variance in making a profit. He can be in the red for 20-30 bets in a row and then in one event "return" his money. Planning with such randomness is very unreliable, isn't it?