Everyone knew BG3 would "a success," but it hasn't just been a success, it's been a nuclear bomb of a success.
Optimistically, people were expecting to get around 1 million in sales. Total. THAT would have been a GREAT SUCCESS. Today I think it has around 10 million on Steam alone, 10x the "hope we get there" number.
Imagine taking a job and hoping for a $10,000 bonus for good performance, and then your boss drops $100,000 on your desk. It's that level of joyful shock.