I recently saw "The Sacred Balance" on PBS, which included a segment about children from Romanian orphanages adopted into the U.S. There was footage of these babies and toddlers in the orphanages, sitting in row upon row of cribs, each alone and with no toys or anything. They all had the same heartbreakingly vacant look in their faces--like people who've been waiting at a bus stop for hours in the cold and have realized the bus is not coming but don't have anywhere else to go.
Then they showed the kids after they'd been in their adoptive homes for a couple of years. They were thriving! One mother who was interviewed said that when her daughter first came to them at 22 months (not walking or talking at all), it was very clear that her only concern was getting fed and cleaned and kept warm, but after a short time, "then WE became important. She saw that we weren't going away, that the same people were going to stay with her and enjoy being with her." and she began to respond with love. It was SO wonderful seeing how this little girl had blossomed!
That, like many other stories about adoption, is evidence that a child can recover from less-than-perfect nurturing in her early life. That doesn't mean there's no point in trying to raise our children the best way we can from the earliest possible stage--it just means that if we do make mistakes, the consequences are not necessarily dire. Young children are very resilient, and older children are less vulnerable, and the effects of some things can be overcome entirely. Other things, while they may have a permanent effect that is in some way negative, don't have to ruin a person's life; nobody is perfect, and our weaknesses may lead us to develop strengths in other areas.
For example, I was thinking just last night that my parents "should have" taught me to jump rope when I was little and/or made an effort, after I discovered that I was very poor at jumping rope, to encourage me to practice and improve. I have a skeletal deformity of the hip joint (first detected when I was 5) that makes it difficult for me to jump with both feet, but I did manage to learn when I was about 14 and had finally gotten enough practice at it. Jumping rope is important socially for girls. Because I "couldn't" do it (and, due to the unfortunate coincidence of being poorly coordinated and slow to learn physical techniques in general, also "couldn't" play those handclapping games or anything with a ball) I was excluded from much of the social activity at recess. My parents' failure to help me develop jumproping and other physical skills had a profound impact on my physical and social development.
Okay, but: Because I was excluded from the other girls' activities, I spent most of my recess time wandering around observing the other kids (both sexes) and learning a lot about them. Watching social interaction as an outsider made it easier for me to see the larger patterns of how people think, behave, and interact. I also gleaned a lot of inside information about people's opinions and plans, because they tended to treat me as invisible and not realize I was listening!
Something my parents DID encourage was my anthropological theorizing about my peers, which we discussed over family dinners. I grew up to become a sociodevelopmental psychologist.
Had I been better at jumping rope, I might've had more fun and been less lonely in elementary school, but I would've missed this opportunity to hone my observational skills and my imagination--when I got bored with just observing, I'd think about how what I was seeing would be different if we lived in Japan, or 100 years ago, or on Mars....
Many of my friends from college also were "unpopular" as kids, for various reasons. Most of us can think of things our parents could have done differently to enable us to function better in the school environment. But every one of those things comes with trade-offs, and the one they all have in common is this: While we might have been "happier" as kids, we would have missed out on the inner strength, the willingness to accept nonconformity, and the motivation to hone individual skills that come from being an outsider.
I do believe that there are experiences one can have in early childhood which, especially if prolonged, CAN ruin a life. Few of them will ruin everyone, because individuals vary in their ability to rebound from various types of harm. But it is possible for the wrong combination of innate temperament and early experiences to produce a psychopath. Fortunately, it doesn't happen very often. Most parenting choices are not 100% good or 100% bad.