Not a math teacher, but I had a boss once when i was younger who constantly would tell me I only did a 99% job. I worked too fast and didn't finish the last little things. It pissed me off every time. He wasn't really that nice about it. He was a pretty blunt and straightforward kinda guy.
He was right though and it took a while but I eventually noticed that I did exactly what he said I was doing and it did impact things I did. Since I realized that, I hear is voice now telling me this before I think I've finished everything I'm doing and inevitably I find something I missed or didn't finish properly. In the end his blunt delivery of information and reasonable criticism did sink in and I feel like my attention to detail has improved because of it on anything I work on now.