You can't stop him. You can only prepare him.
6 seconds sound clip from the How to Train Your Dragon movie soundboard.
You can hear this line at 00:11:16 in the Blu-ray version of the movie.
Quote context
[...]
- Trolls exist. They steal your socks. But only the left ones. What's with that?
- It taught me what a Viking could do. He could crush mountains, level forests, tame seas!
- Even as a boy, I knew what I was, what I had to become.
- You can't stop him. You can only prepare him.
- I know it seems hopeless, but the truth is you won't always be around to protect him.
- He's going to get out there again. He's probably out there now.
- Some people lose their knife or their mug. Not me. I manage to lose an entire dragon.
[...]