She might be unhappy, while he might be completely convinced that she is "the one and only".

当他完全的确信她是他心中的“唯一”时，她也许是不快乐的。

youdao

The purpose of persuasion is make educated person be completely convinced, don't take "major principle" as external demand, turn it into internal needs.

说服的目的是使受教育者心悦诚服，不把“大道理”当作外部要求，而是化为内在需要。

youdao

My caller - who appeared by the way to be completely convinced that he was offering a legitimate product - told me that his firm had lots of satisfied customers.

BBC: A phone call for Mr Sellan