I work 8 hours per day, but the actual time coding is much shorter as everybody in our industry knows: pauses, design moments, checking HN, ... And I'm not a genius, many of my friends are smarter than me. To get something done is basically having some vertical talent (for example ability to code), and putting a steady effort into it for a long time. A fundamental thing is to try to minimize the work to do and to maximize the effect the work has. Just a random examples, Redis has support for transactions, that are quite useful, and are implemented in like ~100 lines of code, because it does not implement rollbacks. The idea is that for the specific data model, operations, and use cases provided by Redis, rollbacks were not important, and that was the case. Getting the design decision wrong, rollbacks could easily introduce 5000 lines of code in Redis and also press other design decisions as a side effect.

EDIT: cloc actually reports 196 lines of code into the file multi.c, but there are additional features including check-and-set that is ~50% of the code, so yep, pretty much 100 lines of code.