I can only relate my own experience with my children. I am indeed hesitant to do so here, as I see the reaction that you have gotten.

First of all, I would like you to remember (as I intend to do) that we, at least most of us, are on Psych Central for various reasons. We're all in a little bit of a pickle with life and so our answers might reflect that.
I hope I don't offend anyone by saying that.

I have four children, now grown. 2 boys, 2 girls.

My girls are not very different from each other. As my oldest was in intensive care, it took me a couple of weeks to bond with her (during which time I suffered from PPD and cried and hated myself and thought that I was somehow a defective mother) But things turned around very quickly. She was the kind of child that everyone adored for some reason.
When my youngest daughter was born, I quickly realized that personalities are indeed very different between siblings. She was not a child that everyone adored, including me. I have no idea why. Even when my kids are together now, there's three and then there's one.

But I am a mom and I am an adult. My first and foremost job is to love my children unconditionally and see to it that they are physically and mentally healthy.
I recognized this personality clash among us (very early on)--but I went out of my way to give my youngest exactly the same amount of time, hugs, kisses, and attention as I did the others--maybe even a little extra.
Frankly, I don't know if she has suffered. I don't know if she ever knew. I would like to think that she doesn't.

I do know that she's perfect.