Everything is genes

Heritability estimates from twin studies are almost always biased downwards. Correcting for some of these can result in significantly larger estimates:

In childhood, parents largely determine a child's life, so there are some environmental effects there, but these typically disappear by adulthood Polderman.

Glibly, then, by the time you're an adult everything is due to genes and luck, and the latter typically shrinks in the long-run.

Sure there some minor exceptions. Common environment unsurprisingly has a decent effect on years of schooling, for instance, but the second order effects are small such that a 1-sd increase in common environment probably increases educational attainment by 0.5~sd, which probably increases adulthood income by about 0.09-sd, which probably increases adulthood happiness by 0.02-sd. Let's liberally suppose the true effect of common environment on adulthood happiness is five times higher: 0.1sd.

Compare to a 1-sd increase in genes, which we'll model as a 0.5-sd statistically independent improvement in the genotypes of the four factors above. My back-of-the-envelope math says that should increase adulthood happiness by about 0.56 sd. Even with quite liberal assumptions, that more than five times the effect size of common environment. If we were measuring it with variance, that 5x would turn into a 25x.

tl;dr - most important objective outcomes in life are determined by genes.