SARS wasn't able to spread nearly as quickly as the novel coronavirus, possibly because of the incubation period and prevalence of asymptotic carriers in this coronavirus.

That wasn't true of SARS which made people very sick so it was able to be contained (it's possibly that the novel coronavirus is just far more contagious but I don't know that for sure).

By mid to late January we all knew this. It was happening in China in full view of the world. The question was whether it could be contained, we didn't know that at the moment. But without extreme intervention it was just simple math that this would happen, and it did.