What crew is your opponent playing?
Terrifying is extremely good... right up until it isn't. It's either the most busted defensive tech in the game, or it does literally nothing for you.
As someone who plays several crews that rely on it (Nightmare, Woe), if I rely on Terrifying to keep my models alive then I'm gonna have a rough time if my opponent has some variance swing their way or if they manage their cards well. What I'm usually looking at is how many good cards they flip on their terrifying duels and how many cards they cheat to pass terrifying. If they cheat to pass terrifying, I'm going to do everything in my power to make them miss or cheat to hit.
It may be helpful to think about it as resource drain, and only spend actions into Terrifying if you know you can afford to cheat enough times to guarantee hits and kills. Sometimes the right play is just to YOLO some swings and hope for the best (never into Nightmare FWIW). Terrifying puts a lot of resource pressure on the opponent, but it's definitely not a silver bullet defense.
Some rules of thumb for playing into terrifying:
Don't cheat the terrifying duel if you can't cheat the attack flip too
It's OK to throw actions at terrifying without cheating, but don't make a plan around your attack succeeding
UNLESS, failing the terrifying duel puts you in a worse position (looking at you Dreamer)
If you know its coming, a single ruthless model goes a long way
Woe, Nightmare, Tormented, Honeypot, are places you know for sure you'll see some terrifying.