Self doubt

I am often plagued with self doubt. I try my best to fight it off, and for the most part it is very much self inflicted, and self-induced. It is hardest to deal with though, when you let something someone else said make you feel that way. I won't go into details about the situation that pushed me there this morning, but I feel completely discouraged. Why is it, that you can be so confident with so many things, but constantly and consistently question your ability as a parent? I adore my children, and feel as though they are smart,lovable and fairly well behaved kids. They are lively, for sure, but that is what a child is supposed to be, full of curiousity and excitement. But when I get one comment from some other parent, whether it be a suggestion or observation, I begin to rethink myself, and my kids. So how do you get around that? My daughter, imp that she is, is driven and passionate, and not easily wrangled, but she says please, and thank you, and is almost always sweet to her brother. When she sets her mind to something though, she can hardly be dissuaded and the end result is a giant tantrum, remedied quickly by a timeout. Once the time out is over, the fit is too. This is a success right? Isn't it? Then why do I feel like such a failure when I have to deal with these tantrums in front of peers or co-workers or worst of all friends without kids? I'm sad that people judge my parenting skills, and sadder still that I let their comments influence my thoughts on my own children. I guess that just leaves me right where I am for the moment, which is sad.