It's just an idiom[1]: > To be confident in or convinced about something's viability, veracity, etc., often to the point of being enthusiastically supportive o

It's just an idiom[1]: > To be confident in or convinced about something's viability, veracity, etc., often to the point of being enthusiastically supportive of it. People on HN seem excited about it. I wanted to learn why, and have received a lot of great responses! [1] https://idioms.thefreedictionary.com/be+sold+on+something https://idioms.thefreedictionary.com/be+sold+on+something