This is the 338th most frequent Bulgarian word.
съвсем
Completely; entirely; quite.
Here, "съвсем" underscores the novelty of the idea.
Тази идея е съвсем нова за мен.
This idea is quite new to me.
"Съвсем" modifies the adverb "неочаквано", emphasizing the unanticipated nature of the arrival.
Тя дойде съвсем неочаквано.
She came entirely unexpectedly.
In this sentence, "съвсем" intensifies the adjective "уверен", specifying the degree of confidence.