Fibonacci Followup

"I want to say this solution is hidden by the way the problem tends to be phrased."

Nope. I was looking around the usual suspects for different descriptions of the Fibonacci problem, and it seems like it's phrased well. Perhaps it's usually found in the "recursive" section of places, which primes you for solving it recursively? This description from structy.net does say "solve this recursively" directly, but that doesn't mean counting backwards from N.

Write a function fib that takes in a number argument, n, and returns the n-th number of the Fibonacci sequence.
 
The 0-th number of the sequence is 0.
 
The 1-st number of the sequence is 1.
 
To generate further numbers of the sequence, calculate the sum of previous two numbers.
 
Solve this recursively.

This leads me to wonder why I would start at the top and count down. Maybe it's intuitive before you learn the optimal solution, but I can't see it now that I know the optimal solution. I'll definitely be paying attention to the way the problems are presented going forward.