Well, with his crappy sword, Vaan can still chain himself, probably by about 2 or (very unlucky) 3 hits. Given his low health, and the general risk involved, it's very easy to accidentally kill himself. Which is why you need good menu opening skills to quickly unequip once again.

I know, power leveling in XII is messed up slightly! Level 90 before the palace? Vaan could've overthrown the empire himself.