In any case, I'm not sure that I need a hint to tell me that doing things quickly and carelessly is a bad idea. But we all do it sometimes, in both our programming and our writing.
I for one would speculate, not to sound harsh, that if you haven't made silly errors like this then you haven't been around the block enough times.
on the other hand, those of us who have been around the block enough times have almost certainly encountered co-workers who were bright, talented, cute, whatever - but at the end of the day were just ... sloppy ... lazy ... careless ... in their approach. It's a personality thing - they had nice childhoods, they never learned to by hyper-vigilant and paranoid, and as a consequence... they write buggy code that can't be trusted.