It’s easy to underestimate how much small, seemingly arbitrary factors shape long-term outcomes - especially when we’re used to telling clean stories about talent, effort, and merit.
I was reminded of this recently while reading Determined by Robert Sapolsky. One striking example he discusses is school entry cutoffs. Because these dates are administrative rather than developmental, children in the same classroom can differ in age by up to ~12 months. In early childhood, that gap often translates into real differences in cognitive, emotional, and self-regulatory maturity.
Teachers may understandably interpret those differences as indicators of ability or potential. That can lead to more encouragement, attention, and higher expectations for slightly older students - advantages that already start compounding by first grade, and can continue through tracking, confidence, and parental responses.
In the UK, where the cutoff date is August 31st, this “relative age effect” shows up clearly in the data. While the effect size decreases over time, it remains detectable on average through secondary school and even into university. It’s a classic example of cumulative advantage (the so-called Matthew Effect). See the attached chart for illustration - it shows a near-perfect linear decline in Oxford graduation rates, with the oldest students (September) being 15% overrepresented and the youngest (August) 15% underrepresented relative to the UK norm.
And of course, school entry dates are just one example. We could start with being born into a middle-class family, in a WEIRD country, at the end of the 20th century which already places you on a very particular starting point in life. And we could keep going. If you want a better sense of the background conditions we tend to leave out of our success (and failure) narratives, Determined is highly recommended - even if you don’t follow Sapolsky all the way on free will.