When you write the code yourself you are slowly building up a mental model of how said thing should work. If you end up introducing a subtle bug during that process, at least you already have a good understanding of the code, so it shouldn't be much of an issue to work backwards to find out what assumptions turned out to be incorrect.

But now with Claude, the mental model of how your code works is not in your head, but resides behind a chain of reasoning from Claude Code that you are not privy too. When something breaks, you either have to spend much longer trying to piece together what your agent has made, or to continue throwing Claude at and hope it doesn't spiral into more subtle bugs.