Well what happens sometimes is girls delude themselves into thinking things are going to be different when they actually aren't.
I have come accross this many times, and it has also been a proven weapon of influence identified by Robert Cialidini in "influence: the psychology of persuasion".
Sometimes our thought process can be really screwed with. See, what can happen is we think we don't want something anymore unless a condition is met. For example a girl won't go back to a guy unless he quits drinking.
Now what can happen is he can pretend he quit drinking, so that the condition is met, and she will be happy convinced things are different.
And here's the kicker: the feeling that things are different and the actions that took place because the conditions were met REMAIN SO even if the original demand is withdrawn.
For example, a few weeks into the relationship he can start drinking again and she will probably not leave him for it.
Why? Who knows! Its the way our brain is wired. Sometimes we make decisions based on certain conditions and we stick to those decisions even if the original conditions are pulled back.
This explains why girls have problems in relationships, break up because of them, then the guy sweet talks them or they "work out" their problems (when in fact theyve just put a temporary band aid on them) and they get back together, only to have the same problems later.
Rinse, Repeat.
Now that you're aware of this psychological weapon of influence, feel free to use it. A lot of people already do without even thinking about it.