Its a fact that the part of your brain that controls your emotions is twice as big as the part that controls logic. What this means in the casino is, when the logical part is telling you to quit, the excited emotional part is telling you go go go, chase your losses, don't stop when you're ahead, go get more cash from the ATM. It completely drowns out the logical part, which is calmly telling you to stop, don't be a fool.
The casinos have known this is how most people play for decades. They didn't know that the emotional part is twice as big, but they could see the results of it right in front of them. The encouraging thing is, you can train yourself not to let the emotions overrun you. Doctors and law enforcement people have to learn to let logic rule and they are very successful at it. The problem is, most gamblers don't want to be logical. They love the emotional roller coster, its why they play. And its why they lose.