Not understanding what is going on with some code or a system you're working on is fundamentally bad. Often, this means bugs, but sometimes it means things work but you don't know how. It's incredibly tempting to call it a day there and finish on that, but a truly disciplined engineer looks further and figures out what is actually going on. You learn more that way and next time you come to that code or system, you're better equipped to change it.
Heads up: As with any terse bit of advice, there will be exceptions of course, and subtleties and nuance that can't possibly be captured in a Byte of Wisdom. This has been what I've experienced, I'd love to hear yours in the comments too!
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