We highly recommend that you read this article from Harvard's Center on the Developing Child. It is a great summary of core capabilities -- falling primarily under the umbrellas of self regulation and executive function -- that everyone needs to truly succeed. And those capabilities are developed in a child's early years:

"The foundation is built in early childhood: By age 3, most children are already using executive function skills in simple ways (e.g., remembering and following simple rules). Ages 3-5 show a remarkable burst of improvement in the proficiency of these skills."

The article also talks about factors that can derail the development of these skills, including:

Serious early adversity and trauma
Chaotic, threatening, or unpredictable environments
Highly rewarding stimuli such as food or drugs
Poverty

It is great insight into the development of our kids and what we are striving to accomplish.