You get a job, you're excited and then success doesn't come as quickly as you thought. It actually starts to become work...what happens next? Do you give up or give in or push through?
That pretty girl says "yes" to a date and you go out then a few months down the road you actually find some things that you don't like...do you move on or realize that loving someone isn't an all or nothing thing?
You start on a diet, you lose weight, but you really like some of the foods you can't eat anymore...what next?
You start to exercise but it loses its luster...
You've worked and worked to get to a certain spot, but then the situation doesn't play out like you thought it should...
You are intoxicated by something and can't get enough, then...you do.
Most of these situations describe trying to change habits.
It is hard to change a habit.