There are any number of traits (Agoraphobia), skills (Intimidation) and devices (Stet Gun) that force Steel tests, and might do so outside of the context of a Firefight or Duel of Wits. However, it’s never clearly explained how such tests are to be handled.
If I were to extrapolate from the rules given for the Firefight, failing a steel test by less than half your hesitation means you hesitate for a test. That is, one action takes place that you can’t resist, if there are any such actions pending. Thus, when your bear of an Anvil Elite get hit by the stet gun and barely loses, his blurred vision clears just after the Vaylen sleepers make a test to take him to their secret lair. On the other hand, failing a test by more than that means you hesitate for a scene. In which case he doesn’t get it together before he has a new endoparasitic friend.
Does that sound right?
A related, though less important matter: Steel test failure within a Duel of Wits isn’t explained very clearly. The scripting sheet lets you select between Swooning, Drooling, etc., but none of those choices are explained in the book, though Burning Wheel explains them in detail.