What secret is this man revealing to his unsuspecting girlfriend?

He gave the woman of his dreams a pendant necklace on their first anniversary of being together!

The pendant necklace was something really special and not just because he had made it with his own two hands, but for what it contained. 

His girlfriend did not discover the true value of the pendant necklace until the following year when, after two years of engagement, during one of their trips, her boyfriend revealed it to her, and put a ring on her finger. 

The first words from her were ---"Are you crazy, and what if I had lost the pendant?". You know, when you think about it, we cannot blame her for this reaction!