In the absence of observations of future events, observation of the past performance of your model is advisable (and rare). If your confidence in the current accuracy of your model is much higher than the past performance of your models... you may be optimizing for something other than accuracy.
observation of the past performance of your model is advisable
Agreed, and in particular on data you did not consider in formulating it.
(and rare).
Citation needed.
Here's the new thread for posting quotes, with the usual rules: