I think the reason that we are very unlikely to rethink the original purpose/process by which we made the decision is that it was slowly and painstakingly made in most cases. Ni and Ti both tend to check and recheck each other's results, so when you finally arrive at a conclusion, it is because all information has been considered, and the reasoning carefully thought out and defined. Therefore, it usually is only new information coming to light that would change our response, not questioning the way we originally arrived at that conclusion.
In the case of immature or insecure reactionary doorslamming, this is perhaps regrettable, but if we're not talking about that, I don't see what the problem is with deciding where you are best to invest your trust and emotional resources with the most safety or return. My problem is usually not drawing that line quickly enough, rather than being overly hasty.