The article is quite clear that it's a totally unreal hypothetical:
Of course, once your investment had grown past a certain
point, it would be impossible to put into any stock
without drastically affecting the stock’s price. In many
cases, investing this volume of cash would be
impossible [...] we also did not take into account
trading fees nor changes in the composition of the S&P
index. We also assumed that all companies allowed for
investment in fractional shares.
Moreover, even if one made the impossibly optimistic
assumption that picking the best stock of the day is a
50-50 guess, there would be only a one-in-3.53
trevigintillion (3.53 x 1072) chance of matching these
results.
There's another humorous follow up on Quartz, positing that "[i]nvesting a day late every day would have returned 19.6% in 2013".[0]
A lot of people here seem very upset that this isn't a recipe they can follow to riches. Clearly this is just an exercise illustrating wild growth, and an interesting article. No need for people to be so bitter.
[0] http://qz.com/158489/investing-a-day-late-every-day-would-ha...
Edit: spelling.