Well, yesterday I made a rather significant change to the code. Essentially, a reimplementation of an existing function in a completely different way, to avoid a memory consumption issue that cannot be solved in the old approach. 68 insertions, 15 deletions. It, unexpectedly, worked correctly and passed all tests from the first attempt, even though there are threads involved, and they are my weak point. But I didn't have a "Huh... that's pretty cool" moment. I had an "I don't like this code, it's too complex, it must be wrong somehow" moment.