It isn't in my experience. Understanding code that you did not write for a problem that you do not fully grasp is a lot of work. It's hard enough when you did write the code and when you do fully grasp the problem, which you'd have to if you were to write it yourself. Typically that's what first draft code is for: to see if you actually understand the problem.
With a brain you can also build it piece by piece, in fact I don't know of any other way of writing a large software system than doing it piece by piece.
