Runaway

"They say he is a tall muscular man with arms the size of boulders with the strength of catapults. But that ain't even the worst part, they also say he rides two of the most powerful and feared dragons of them all, Night Furies. Every island he settles in he carries a herd of dragons behind him, whoever defies him will never return."

After Gothi picked him to slay the red and very much angry Monstrous Nightmare he gazed at the bolts and leather he used for Toothless' saddle and decided.

If he did stay and kill that dragon

He would be betraying his only and greatest friend.