The engineering team had approximately 3 hours notice prior to a teleconference to make a presentation. The telecon occurred the evening before launch, with a midnight deadline for the go / nogo decision to be made.
Due to the short timescale to build their presentation, they re-used info from existing presentations. Unfortunately, the same info had previously been used to demonstrate why their o-rings were safe. The NASA people basically said, 'last time you showed me this graph it meant things were safe, this time it means things are dangerous. What gives?'
The decision makers were looking for excuses to move forward, and that gave them an excuse to ignore the warnings.