300,000 lines of code doesn't seem unattainable for a single developer in a year. If I'm in the zone, I can easily bang out 5-10k lines of code over a weekend if I know what I want to write.

But that's the thing: a lot of development involves not writing any code, as you re-think your abstractions, plan the architecture of the next bits you'll write, debug what you've written, etc.

So I don't think we're necessarily talking about speed when we say that it's harder to read code than to write it. I think reading -- and truly understanding -- code (especially when it's someone else's, or even yours, that you haven't seen in a long time) can require quite a bit more mental effort than writing code.

Interesting. I usually think about it at a different scale; its much easier to write something small and clever than it is to read and understand it later.

What language do you use? In UI you can reach that 300k loc quite quickly.