Aggressiveness may be a good thing when you are fighting your enemy on the battlefield, but it rarely helps in gambling. I'm saying "rarely" instead of "never" because in some extremely rare cases people do win because of their aggressive behaviour. It happens by chance, like those cases when people hit the Jackpot in a lottery, but it happens and it would be wrong to say that people always lose because of their aggressiveness. Most of the time, however, people lose and lose really big amounts when they start acting like that. Be cool and enjoy your gambling experience without going over the edge, that's what I would say to beginners if they want to stay out of gambling addiction.
I agree with that because I have seen people experience such things. When a gambler starts losing or lose their initial bankroll, they come back with a bigger bankroll and start betting aggressively, what happens is sometimes they manage to win and recover the money they have lost earlier, but most of the time, they lose what they have brought the second time or even if they bring more after that because you can't win all the time.
Aggressive bettors manage to win big if one of their bets hit something big like if someone is betting with a large bet in a slot game and they manage to hit 3000x or more, they will get a lot of money out of that, but that doesn't happen very often and most people will eventually be at the losing side.