We are all products of our history and learning. There's a parental legacy that has been passed on to you, based on how your mother mothered you and your father fathered you. You bring this cumulative experience to the role of motherhood.
Your parents raised you a certain way, and as a parent you are likely affected by those experiences in one of two ways. The most common reaction is to do exactly what your parents did. If they were yellers and screamers, odds are that you are as well. If they were cold, withdrawn, and totally absorbed in other aspects of their own lives, neglecting yours, then you probably behave in the same fashion. If they lived vicariously through you as a "second time around" for them, you probably now live the legacy by standing on the sidelines at every Little League game, screaming like a loudmouth—can you tell that really bugs me?—or being an obnoxious stage mom at the local yokel beauty contest. Not good! But if your parents made sure to come in together to tuck you in and kiss you every night at bedtime, and you do the same with your children, you've learned something great there.
The second common response is to rebel against the experience and behave in a radically different way. In reaction to being raised with yelling and screaming, you may be the nicest, sweetest, and most lenient parent you could ever imagine. Sounds perfect, but nothing extreme ever is. This opposite reaction may cause you to be overindulgent and spoil your children, a behavior that often leads to poor impulse control in kids, misbehavior, and even low academic performance.
Good or bad, right or wrong, your family in general and your parents in particular wrote on the blank slate that is you. It's impossible to overemphasize the power of this legacy. And only when you put your own childhood under the microscope can you start to make some conscious, here-and-now choices about how you raise your children, rather than being mindlessly controlled by your past.