That, and being able to walk away when things are going badly.
Obviously I am discussing recreational gamblers and not AP's as there is no way to AP craps.
As I EXPECT to lose at craps, or slots, I approach it as a hobby with a cost attached to it, and I don't want the cost to exceed the value of the entertainment which playing the games affords me.
The goal of gambling within set limits can be tough to realize due to the addictive nature of casino games.