[thesz]

Most of the software engineers out there do the support, augmenting source code behemoths the least possible way to achieve desired outcome. I believe that more than 90% of software development was support roles as early as 2K or so.

Not that I had an opportunity to write new code, but most of my work through my experience was either to fix bugs or to add new functionality to an existing system with as little code as possible. Both goals mean reuse and understanding of the existing code. For both "reuse" and "understanding" you have to thoroughly read existing code a dozen or so times over.

Tests (in TDD) can show you presence of bugs, not the absence of them. For the absence of bugs one has to thoroughly know problem domain and source code solving the problems.