Let me give an example, although it's not about good or bad behavior... it does have to do with what seems to be the primary concern of parents of babies: sleep.

Day 2 of my first child's life: The baby books say she should be sleeping around 18 hours a day.  She is sleeping only 12 hours a day.  (She still has problems sleeping at age 4 and never sleeps through the night.)

Day 2 of my second child's life: He is sleeping 23 hours a day and I keep asking my mom if this qualifies as "lethargic" and should we call the doctor?  (He slept through the night at 1 month of age.)

Parenting books are chock full of advice on what to do to get your baby sleeping properly-- they call this, I kid you not, "sleep hygiene."

And here I have two kids that are on opposite ends of the spectrum and it has absolutely nothing to do with any action on my part.

Personally, I think environmental factors are totally over-emphasized, because parenting has become a major industry, and how can you sell books, videos, toys, and gadgets if you don't convince parents that their children are nothing but a product of their parenting?