Unfortunately, not everybody has this realization. Some people go on contradicting themselves, not realizing they're losing people's confidence in them. These are the true hypocrites--the ones who pay so little attention to what they say or how their words and actions may appear to others that they never realize that they are defeating the very image of themselves they are trying to project.
In spite of myself, I catch my own hypocrisy from time to time. In trying to win an argument, I sometimes end up changing my mind from the beginning to the end. It's not a conscious choice, or manipulation, but rather ignorance. Ignorance about the issues to the point that I am not allied to one side of things more than the other and I trip over my words.
Hypocrisy stems from ignorance. We say we agree with one thing, but it's more for the principle of the issue than because we have examined it and honestly hold it to be true. In cases like this, ambivalence, or agnosticism (I mean this in a broad sense), is a better option than risking hypocrisy by allying oneself to side of an issue and then going back on your half-hearted belief.
The best option is always to examine things. Discuss them, learn about them, get a good grasp on the issue before you automatically say I agree or I disagree. Then, when confronted with it, in an argument or just in your daily life, you can see more clearly the choices you make, the words you choose. You won't have to try so hard to argue your point, because you will know the facts and details of your beliefs so well that you can explain them to anyone.
I've said it before, I'll say it again: An unexamined life is not worth living. Don't let yourself wander into hypocrisy merely because you have not taken the time to consider the matter thoroughly enough.
Reserve the right to change your mind--just not too often.