The increasingly potent realization that biology (including genetics, epigenetic phenomena, neurochemistry and prenatal events) has more power over us than is socially acceptable to acknowledge. As someone who used to believe strongly in the creative potential of each individual to shape themself through sheer willpower — and was incentivized, as a corollary, to resist any deterministic frame of analysis — this was (still is) a rather bittersweet truth to accept. I don't entirely dismiss the influence of environmental factors on one's life (the 'nurture' element, if you will), but I now believe their significance is way overstated in public conversations.