[josephg]

The cost is also in debugging. It’s much harder to figure out a problem after the fact because you’ve forgotten how the code in question works. If you catch a mistake while you’re coding something up, you can fix it immediately and not give it a second thought. But if you need to track a bug down weeks or months after writing the code, it can take a lot of work to figure out what the code does (and why), and why it is behaving incorrectly.

I’ve lost weeks to a memory leak once in javascript that was a 2 line change to fix. If I realised the problem when I wrote the code, I would have saved myself a lot of trouble.