This, we say -
This, we say, was unexpected. The question becomes: why?
We use "why" here in a double sense. It defines both the sentiment and the sentimental.
Why are we surprised? (generally)
Why did this surprise us? (specifically)
The answer to both questions, we find, is the same.
The familiar has become strange.
The traditional has become radical.
If a thing is completely outside of our experience, and we know that, it cannot surprise us. It cannot shock us. We must have an expectation for that expectation to be violated.
The unexpected requires the transformation of the expected into an unfamiliar form, and it requires that transformation to happen off-stage: either at a literal distance, or at a distance of inattention. Sentiment serves as the boundary between stage and wings: it preserves the expected within the darkness of memory until the spotlight of reconsideration lays bare the evolution (as revolution) that has taken place.
We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.