Without being too familiar with the subject - another commenter referred to the "swiss cheese model": the O-ring design, the temperature etc. weren't the single cause, they were contributing factors, and the more contributing factors you eliminate, the more certain you can be that you won't have a repeat accident. AFAIK there weren't any more Shuttle launches at such low temperatures after that anymore either?

That's right, the accident launch was by far the coldest. They also added joint heaters.