You were 本来 originally going to go grab the 本 notebook from the bookshelf, but it spontaneously floated off and 来 came to you! You 本来 originally had no idea your 本 notebook could 来 come to you like this. Now you know.
Usage
本来 的 意思
original meaning
她 本来 明年 想 去 台湾。
She originally was thinking to go to Taiwan next year.